From 5fd13d80a87c9015b8691bb35145371f50b06e39 Mon Sep 17 00:00:00 2001
From: Buyaa Namnan <bunamnan@microsoft.com>
Date: Tue, 7 Jan 2020 14:51:14 -0800
Subject: [PATCH 1/6] Annotate System.Security.Claims for nullable

---
 .../ref/System.Security.Claims.cs             |  92 +++++++-------
 .../ref/System.Security.Claims.csproj         |   1 +
 .../src/System.Security.Claims.csproj         |   1 +
 .../src/System/Security/Claims/Claim.cs       |  54 ++++-----
 .../System/Security/Claims/ClaimsIdentity.cs  | 114 +++++++++---------
 .../System/Security/Claims/ClaimsPrincipal.cs |  40 +++---
 .../System/Security/Claims/GenericIdentity.cs |   6 +-
 .../Security/Claims/GenericPrincipal.cs       |  10 +-
 8 files changed, 160 insertions(+), 158 deletions(-)

diff --git a/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs b/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs
index 54ab521ae75ccc..781c9899845d7c 100644
--- a/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs
+++ b/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs
@@ -10,27 +10,27 @@ namespace System.Security.Claims
     public partial class Claim
     {
         public Claim(System.IO.BinaryReader reader) { }
-        public Claim(System.IO.BinaryReader reader, System.Security.Claims.ClaimsIdentity subject) { }
+        public Claim(System.IO.BinaryReader reader, System.Security.Claims.ClaimsIdentity? subject) { }
         protected Claim(System.Security.Claims.Claim other) { }
-        protected Claim(System.Security.Claims.Claim other, System.Security.Claims.ClaimsIdentity subject) { }
+        protected Claim(System.Security.Claims.Claim other, System.Security.Claims.ClaimsIdentity? subject) { }
         public Claim(string type, string value) { }
-        public Claim(string type, string value, string valueType) { }
-        public Claim(string type, string value, string valueType, string issuer) { }
-        public Claim(string type, string value, string valueType, string issuer, string originalIssuer) { }
-        public Claim(string type, string value, string valueType, string issuer, string originalIssuer, System.Security.Claims.ClaimsIdentity subject) { }
-        protected virtual byte[] CustomSerializationData { get { throw null; } }
+        public Claim(string type, string value, string? valueType) { }
+        public Claim(string type, string value, string? valueType, string? issuer) { }
+        public Claim(string type, string value, string? valueType, string? issuer, string? originalIssuer) { }
+        public Claim(string type, string value, string? valueType, string? issuer, string? originalIssuer, System.Security.Claims.ClaimsIdentity? subject) { }
+        protected virtual byte[]? CustomSerializationData { get { throw null; } }
         public string Issuer { get { throw null; } }
         public string OriginalIssuer { get { throw null; } }
-        public System.Collections.Generic.IDictionary<string, string> Properties { get { throw null; } }
-        public System.Security.Claims.ClaimsIdentity Subject { get { throw null; } }
+        public System.Collections.Generic.IDictionary<string, string?> Properties { get { throw null; } }
+        public System.Security.Claims.ClaimsIdentity? Subject { get { throw null; } }
         public string Type { get { throw null; } }
         public string Value { get { throw null; } }
         public string ValueType { get { throw null; } }
         public virtual System.Security.Claims.Claim Clone() { throw null; }
-        public virtual System.Security.Claims.Claim Clone(System.Security.Claims.ClaimsIdentity identity) { throw null; }
+        public virtual System.Security.Claims.Claim Clone(System.Security.Claims.ClaimsIdentity? identity) { throw null; }
         public override string ToString() { throw null; }
         public virtual void WriteTo(System.IO.BinaryWriter writer) { }
-        protected virtual void WriteTo(System.IO.BinaryWriter writer, byte[] userData) { }
+        protected virtual void WriteTo(System.IO.BinaryWriter writer, byte[]? userData) { }
     }
     public partial class ClaimsIdentity : System.Security.Principal.IIdentity
     {
@@ -38,43 +38,43 @@ public partial class ClaimsIdentity : System.Security.Principal.IIdentity
         public const string DefaultNameClaimType = "http://schemas.xmlsoap.org/ws/2005/05/identity/claims/name";
         public const string DefaultRoleClaimType = "http://schemas.microsoft.com/ws/2008/06/identity/claims/role";
         public ClaimsIdentity() { }
-        public ClaimsIdentity(System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> claims) { }
-        public ClaimsIdentity(System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> claims, string authenticationType) { }
-        public ClaimsIdentity(System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> claims, string authenticationType, string nameType, string roleType) { }
+        public ClaimsIdentity(System.Collections.Generic.IEnumerable<System.Security.Claims.Claim>? claims) { }
+        public ClaimsIdentity(System.Collections.Generic.IEnumerable<System.Security.Claims.Claim>? claims, string? authenticationType) { }
+        public ClaimsIdentity(System.Collections.Generic.IEnumerable<System.Security.Claims.Claim>? claims, string? authenticationType, string? nameType, string? roleType) { }
         public ClaimsIdentity(System.IO.BinaryReader reader) { }
         protected ClaimsIdentity(System.Runtime.Serialization.SerializationInfo info) { }
         protected ClaimsIdentity(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         protected ClaimsIdentity(System.Security.Claims.ClaimsIdentity other) { }
-        public ClaimsIdentity(System.Security.Principal.IIdentity identity) { }
-        public ClaimsIdentity(System.Security.Principal.IIdentity identity, System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> claims) { }
-        public ClaimsIdentity(System.Security.Principal.IIdentity identity, System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> claims, string authenticationType, string nameType, string roleType) { }
-        public ClaimsIdentity(string authenticationType) { }
-        public ClaimsIdentity(string authenticationType, string nameType, string roleType) { }
-        public System.Security.Claims.ClaimsIdentity Actor { get { throw null; } set { } }
-        public virtual string AuthenticationType { get { throw null; } }
-        public object BootstrapContext { get { throw null; } set { } }
-        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> Claims { get { throw null; } }
-        protected virtual byte[] CustomSerializationData { get { throw null; } }
+        public ClaimsIdentity(System.Security.Principal.IIdentity? identity) { }
+        public ClaimsIdentity(System.Security.Principal.IIdentity? identity, System.Collections.Generic.IEnumerable<System.Security.Claims.Claim>? claims) { }
+        public ClaimsIdentity(System.Security.Principal.IIdentity? identity, System.Collections.Generic.IEnumerable<System.Security.Claims.Claim>? claims, string? authenticationType, string? nameType, string? roleType) { }
+        public ClaimsIdentity(string? authenticationType) { }
+        public ClaimsIdentity(string? authenticationType, string? nameType, string? roleType) { }
+        public System.Security.Claims.ClaimsIdentity? Actor { get { throw null; } set { } }
+        public virtual string? AuthenticationType { get { throw null; } }
+        public object? BootstrapContext { get { throw null; } set { } }
+        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> Claims { get { throw null; } }
+        protected virtual byte[]? CustomSerializationData { get { throw null; } }
         public virtual bool IsAuthenticated { get { throw null; } }
-        public string Label { get { throw null; } set { } }
-        public virtual string Name { get { throw null; } }
+        public string? Label { get { throw null; } set { } }
+        public virtual string? Name { get { throw null; } }
         public string NameClaimType { get { throw null; } }
         public string RoleClaimType { get { throw null; } }
         public virtual void AddClaim(System.Security.Claims.Claim claim) { }
         public virtual void AddClaims(System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> claims) { }
         public virtual System.Security.Claims.ClaimsIdentity Clone() { throw null; }
         protected virtual System.Security.Claims.Claim CreateClaim(System.IO.BinaryReader reader) { throw null; }
-        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> FindAll(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
+        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> FindAll(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
         public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> FindAll(string type) { throw null; }
-        public virtual System.Security.Claims.Claim FindFirst(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
-        public virtual System.Security.Claims.Claim FindFirst(string type) { throw null; }
+        public virtual System.Security.Claims.Claim? FindFirst(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
+        public virtual System.Security.Claims.Claim? FindFirst(string type) { throw null; }
         protected virtual void GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
-        public virtual bool HasClaim(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
+        public virtual bool HasClaim(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
         public virtual bool HasClaim(string type, string value) { throw null; }
-        public virtual void RemoveClaim(System.Security.Claims.Claim claim) { }
-        public virtual bool TryRemoveClaim(System.Security.Claims.Claim claim) { throw null; }
+        public virtual void RemoveClaim(System.Security.Claims.Claim? claim) { }
+        public virtual bool TryRemoveClaim(System.Security.Claims.Claim? claim) { throw null; }
         public virtual void WriteTo(System.IO.BinaryWriter writer) { }
-        protected virtual void WriteTo(System.IO.BinaryWriter writer, byte[] userData) { }
+        protected virtual void WriteTo(System.IO.BinaryWriter writer, byte[]? userData) { }
     }
     public partial class ClaimsPrincipal : System.Security.Principal.IPrincipal
     {
@@ -84,27 +84,27 @@ public ClaimsPrincipal(System.IO.BinaryReader reader) { }
         protected ClaimsPrincipal(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         public ClaimsPrincipal(System.Security.Principal.IIdentity identity) { }
         public ClaimsPrincipal(System.Security.Principal.IPrincipal principal) { }
-        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> Claims { get { throw null; } }
+        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> Claims { get { throw null; } }
         public static System.Func<System.Security.Claims.ClaimsPrincipal> ClaimsPrincipalSelector { get { throw null; } set { } }
-        public static System.Security.Claims.ClaimsPrincipal Current { get { throw null; } }
-        protected virtual byte[] CustomSerializationData { get { throw null; } }
+        public static System.Security.Claims.ClaimsPrincipal? Current { get { throw null; } }
+        protected virtual byte[]? CustomSerializationData { get { throw null; } }
         public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.ClaimsIdentity> Identities { get { throw null; } }
-        public virtual System.Security.Principal.IIdentity Identity { get { throw null; } }
-        public static System.Func<System.Collections.Generic.IEnumerable<System.Security.Claims.ClaimsIdentity>, System.Security.Claims.ClaimsIdentity> PrimaryIdentitySelector { get { throw null; } set { } }
+        public virtual System.Security.Principal.IIdentity? Identity { get { throw null; } }
+        public static System.Func<System.Collections.Generic.IEnumerable<System.Security.Claims.ClaimsIdentity>, System.Security.Claims.ClaimsIdentity?> PrimaryIdentitySelector { get { throw null; } set { } }
         public virtual void AddIdentities(System.Collections.Generic.IEnumerable<System.Security.Claims.ClaimsIdentity> identities) { }
         public virtual void AddIdentity(System.Security.Claims.ClaimsIdentity identity) { }
         public virtual System.Security.Claims.ClaimsPrincipal Clone() { throw null; }
         protected virtual System.Security.Claims.ClaimsIdentity CreateClaimsIdentity(System.IO.BinaryReader reader) { throw null; }
-        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> FindAll(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
+        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> FindAll(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
         public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> FindAll(string type) { throw null; }
-        public virtual System.Security.Claims.Claim FindFirst(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
-        public virtual System.Security.Claims.Claim FindFirst(string type) { throw null; }
+        public virtual System.Security.Claims.Claim? FindFirst(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
+        public virtual System.Security.Claims.Claim? FindFirst(string type) { throw null; }
         protected virtual void GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
-        public virtual bool HasClaim(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
+        public virtual bool HasClaim(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
         public virtual bool HasClaim(string type, string value) { throw null; }
         public virtual bool IsInRole(string role) { throw null; }
         public virtual void WriteTo(System.IO.BinaryWriter writer) { }
-        protected virtual void WriteTo(System.IO.BinaryWriter writer, byte[] userData) { }
+        protected virtual void WriteTo(System.IO.BinaryWriter writer, byte[]? userData) { }
     }
     public static partial class ClaimTypes
     {
@@ -202,15 +202,15 @@ protected GenericIdentity(System.Security.Principal.GenericIdentity identity) {
         public GenericIdentity(string name) { }
         public GenericIdentity(string name, string type) { }
         public override string AuthenticationType { get { throw null; } }
-        public override System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> Claims { get { throw null; } }
+        public override System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> Claims { get { throw null; } }
         public override bool IsAuthenticated { get { throw null; } }
         public override string Name { get { throw null; } }
         public override System.Security.Claims.ClaimsIdentity Clone() { throw null; }
     }
     public partial class GenericPrincipal : System.Security.Claims.ClaimsPrincipal
     {
-        public GenericPrincipal(System.Security.Principal.IIdentity identity, string[] roles) { }
+        public GenericPrincipal(System.Security.Principal.IIdentity identity, string[]? roles) { }
         public override System.Security.Principal.IIdentity Identity { get { throw null; } }
-        public override bool IsInRole(string role) { throw null; }
+        public override bool IsInRole(string? role) { throw null; }
     }
 }
diff --git a/src/libraries/System.Security.Claims/ref/System.Security.Claims.csproj b/src/libraries/System.Security.Claims/ref/System.Security.Claims.csproj
index f50b03583ce946..644919c10192bd 100644
--- a/src/libraries/System.Security.Claims/ref/System.Security.Claims.csproj
+++ b/src/libraries/System.Security.Claims/ref/System.Security.Claims.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <Configurations>$(NetCoreAppCurrent)-Debug;$(NetCoreAppCurrent)-Release</Configurations>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Security.Claims.cs" />
diff --git a/src/libraries/System.Security.Claims/src/System.Security.Claims.csproj b/src/libraries/System.Security.Claims/src/System.Security.Claims.csproj
index 1158601bc31e31..12c7885a9f2c6b 100644
--- a/src/libraries/System.Security.Claims/src/System.Security.Claims.csproj
+++ b/src/libraries/System.Security.Claims/src/System.Security.Claims.csproj
@@ -2,6 +2,7 @@
   <PropertyGroup>
     <AssemblyName>System.Security.Claims</AssemblyName>
     <Configurations>$(NetCoreAppCurrent)-Debug;$(NetCoreAppCurrent)-Release</Configurations>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Security\Claims\Claim.cs" />
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/Claim.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/Claim.cs
index 785383437176bf..7a64b9dcf4d130 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/Claim.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/Claim.cs
@@ -27,13 +27,13 @@ private enum SerializationMask
             UserData = 128,
         }
 
-        private readonly byte[] _userSerializationData;
+        private readonly byte[]? _userSerializationData;
 
         private readonly string _issuer;
         private readonly string _originalIssuer;
-        private Dictionary<string, string> _properties;
+        private Dictionary<string, string?>? _properties;
 
-        private readonly ClaimsIdentity _subject;
+        private readonly ClaimsIdentity? _subject;
         private readonly string _type;
         private readonly string _value;
         private readonly string _valueType;
@@ -56,7 +56,7 @@ public Claim(BinaryReader reader)
         /// <param name="reader">a <see cref="BinaryReader"/> pointing to a <see cref="Claim"/>.</param>
         /// <param name="subject"> the value for <see cref="Claim.Subject"/>, which is the <see cref="ClaimsIdentity"/> that has these claims.</param>
         /// <exception cref="ArgumentNullException">if 'reader' is null.</exception>
-        public Claim(BinaryReader reader, ClaimsIdentity subject)
+        public Claim(BinaryReader reader, ClaimsIdentity? subject)
         {
             if (reader == null)
             {
@@ -157,7 +157,7 @@ public Claim(BinaryReader reader, ClaimsIdentity subject)
         /// <seealso cref="ClaimTypes"/>
         /// <seealso cref="ClaimValueTypes"/>
         public Claim(string type, string value)
-            : this(type, value, ClaimValueTypes.String, ClaimsIdentity.DefaultIssuer, ClaimsIdentity.DefaultIssuer, (ClaimsIdentity)null)
+            : this(type, value, ClaimValueTypes.String, ClaimsIdentity.DefaultIssuer, ClaimsIdentity.DefaultIssuer, (ClaimsIdentity?)null)
         {
         }
 
@@ -176,8 +176,8 @@ public Claim(string type, string value)
         /// <seealso cref="ClaimsIdentity"/>
         /// <seealso cref="ClaimTypes"/>
         /// <seealso cref="ClaimValueTypes"/>
-        public Claim(string type, string value, string valueType)
-            : this(type, value, valueType, ClaimsIdentity.DefaultIssuer, ClaimsIdentity.DefaultIssuer, (ClaimsIdentity)null)
+        public Claim(string type, string value, string? valueType)
+            : this(type, value, valueType, ClaimsIdentity.DefaultIssuer, ClaimsIdentity.DefaultIssuer, (ClaimsIdentity?)null)
         {
         }
 
@@ -196,8 +196,8 @@ public Claim(string type, string value, string valueType)
         /// <seealso cref="ClaimsIdentity"/>
         /// <seealso cref="ClaimTypes"/>
         /// <seealso cref="ClaimValueTypes"/>
-        public Claim(string type, string value, string valueType, string issuer)
-            : this(type, value, valueType, issuer, issuer, (ClaimsIdentity)null)
+        public Claim(string type, string value, string? valueType, string? issuer)
+            : this(type, value, valueType, issuer, issuer, (ClaimsIdentity?)null)
         {
         }
 
@@ -216,8 +216,8 @@ public Claim(string type, string value, string valueType, string issuer)
         /// <seealso cref="ClaimsIdentity"/>
         /// <seealso cref="ClaimTypes"/>
         /// <seealso cref="ClaimValueTypes"/>
-        public Claim(string type, string value, string valueType, string issuer, string originalIssuer)
-            : this(type, value, valueType, issuer, originalIssuer, (ClaimsIdentity)null)
+        public Claim(string type, string value, string? valueType, string? issuer, string? originalIssuer)
+            : this(type, value, valueType, issuer, originalIssuer, (ClaimsIdentity?)null)
         {
         }
 
@@ -234,7 +234,7 @@ public Claim(string type, string value, string valueType, string issuer, string
         /// <seealso cref="ClaimsIdentity"/>
         /// <seealso cref="ClaimTypes"/>
         /// <seealso cref="ClaimValueTypes"/>
-        public Claim(string type, string value, string valueType, string issuer, string originalIssuer, ClaimsIdentity subject)
+        public Claim(string type, string value, string? valueType, string? issuer, string? originalIssuer, ClaimsIdentity? subject)
             : this(type, value, valueType, issuer, originalIssuer, subject, null, null)
         {
         }
@@ -251,7 +251,7 @@ public Claim(string type, string value, string valueType, string issuer, string
         /// <param name="subject">The subject that this claim describes.</param>
         /// <param name="propertyKey">This allows adding a property when adding a Claim.</param>
         /// <param name="propertyValue">The value associated with the property.</param>
-        internal Claim(string type, string value, string valueType, string issuer, string originalIssuer, ClaimsIdentity subject, string propertyKey, string propertyValue)
+        internal Claim(string type, string value, string? valueType, string? issuer, string? originalIssuer, ClaimsIdentity? subject, string? propertyKey, string? propertyValue)
         {
             if (type == null)
             {
@@ -272,7 +272,7 @@ internal Claim(string type, string value, string valueType, string issuer, strin
 
             if (propertyKey != null)
             {
-                _properties = new Dictionary<string, string>();
+                _properties = new Dictionary<string, string?>();
                 _properties[propertyKey] = propertyValue;
             }
         }
@@ -284,7 +284,7 @@ internal Claim(string type, string value, string valueType, string issuer, strin
         /// <remarks><see cref="Claim.Subject"/>will be set to 'null'.</remarks>
         /// <exception cref="ArgumentNullException">if 'other' is null.</exception>
         protected Claim(Claim other)
-            : this(other, (other == null ? (ClaimsIdentity)null : other._subject))
+            : this(other, (other == null ? (ClaimsIdentity?)null : other._subject))
         {
         }
 
@@ -295,7 +295,7 @@ protected Claim(Claim other)
         /// <param name="subject">the <see cref="ClaimsIdentity"/> to assign to <see cref="Claim.Subject"/>.</param>
         /// <remarks><see cref="Claim.Subject"/>will be set to 'subject'.</remarks>
         /// <exception cref="ArgumentNullException">if 'other' is null.</exception>
-        protected Claim(Claim other, ClaimsIdentity subject)
+        protected Claim(Claim other, ClaimsIdentity? subject)
         {
             if (other == null)
                 throw new ArgumentNullException(nameof(other));
@@ -308,7 +308,7 @@ protected Claim(Claim other, ClaimsIdentity subject)
             _valueType = other._valueType;
             if (other._properties != null)
             {
-                _properties = new Dictionary<string, string>(other._properties);
+                _properties = new Dictionary<string, string?>(other._properties);
             }
 
             if (other._userSerializationData != null)
@@ -320,7 +320,7 @@ protected Claim(Claim other, ClaimsIdentity subject)
         /// <summary>
         /// Contains any additional data provided by a derived type, typically set when calling <see cref="WriteTo(BinaryWriter, byte[])"/>.
         /// </summary>
-        protected virtual byte[] CustomSerializationData
+        protected virtual byte[]? CustomSerializationData
         {
             get
             {
@@ -352,13 +352,13 @@ public string OriginalIssuer
         /// <summary>
         /// Gets the collection of Properties associated with the <see cref="Claim"/>.
         /// </summary>
-        public IDictionary<string, string> Properties
+        public IDictionary<string, string?> Properties
         {
             get
             {
                 if (_properties == null)
                 {
-                    _properties = new Dictionary<string, string>();
+                    _properties = new Dictionary<string, string?>();
                 }
                 return _properties;
             }
@@ -367,7 +367,7 @@ public IDictionary<string, string> Properties
         /// <summary>
         /// Gets the subject of the <see cref="Claim"/>.
         /// </summary>
-        public ClaimsIdentity Subject
+        public ClaimsIdentity? Subject
         {
             get { return _subject; }
         }
@@ -403,7 +403,7 @@ public string ValueType
         /// </summary>
         public virtual Claim Clone()
         {
-            return Clone((ClaimsIdentity)null);
+            return Clone((ClaimsIdentity?)null);
         }
 
         /// <summary>
@@ -411,7 +411,7 @@ public virtual Claim Clone()
         /// </summary>
         /// <param name="identity">the value for <see cref="Claim.Subject"/>, which is the <see cref="ClaimsIdentity"/> that has these claims.</param>
         /// <remarks><see cref="Claim.Subject"/> will be set to 'identity'.</remarks>
-        public virtual Claim Clone(ClaimsIdentity identity)
+        public virtual Claim Clone(ClaimsIdentity? identity)
         {
             return new Claim(this, identity);
         }
@@ -432,7 +432,7 @@ public virtual void WriteTo(BinaryWriter writer)
         /// <param name="writer">the <see cref="BinaryWriter"/> to use for data storage.</param>
         /// <param name="userData">additional data provided by derived type.</param>
         /// <exception cref="ArgumentNullException">if 'writer' is null.</exception>
-        protected virtual void WriteTo(BinaryWriter writer, byte[] userData)
+        protected virtual void WriteTo(BinaryWriter writer, byte[]? userData)
         {
             if (writer == null)
             {
@@ -514,17 +514,17 @@ protected virtual void WriteTo(BinaryWriter writer, byte[] userData)
 
             if ((mask & SerializationMask.HasProperties) == SerializationMask.HasProperties)
             {
-                writer.Write(_properties.Count);
+                writer.Write(_properties!.Count);
                 foreach (var kvp in _properties)
                 {
                     writer.Write(kvp.Key);
-                    writer.Write(kvp.Value);
+                    writer.Write(kvp.Value!);
                 }
             }
 
             if ((mask & SerializationMask.UserData) == SerializationMask.UserData)
             {
-                writer.Write(userData.Length);
+                writer.Write(userData!.Length);
                 writer.Write(userData);
             }
 
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
index 93c67bd66fe009..4924e51df48f9e 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
@@ -27,13 +27,13 @@ private enum SerializationMask
             UserData = 128,
         }
 
-        private byte[] _userSerializationData;
-        private ClaimsIdentity _actor;
-        private string _authenticationType;
-        private object _bootstrapContext;
-        private List<List<Claim>> _externalClaims;
-        private string _label;
-        private readonly List<Claim> _instanceClaims = new List<Claim>();
+        private byte[]? _userSerializationData;
+        private ClaimsIdentity? _actor;
+        private string? _authenticationType;
+        private object? _bootstrapContext;
+        private List<List<Claim>>? _externalClaims;
+        private string? _label;
+        private readonly List<Claim?> _instanceClaims = new List<Claim?>();
         private string _nameClaimType = DefaultNameClaimType;
         private string _roleClaimType = DefaultRoleClaimType;
 
@@ -50,7 +50,7 @@ private enum SerializationMask
         /// Initializes an instance of <see cref="ClaimsIdentity"/>.
         /// </summary>
         public ClaimsIdentity()
-            : this((IIdentity)null, (IEnumerable<Claim>)null, (string)null, (string)null, (string)null)
+            : this((IIdentity?)null, (IEnumerable<Claim>?)null, (string?)null, (string?)null, (string?)null)
         {
         }
 
@@ -59,8 +59,8 @@ public ClaimsIdentity()
         /// </summary>
         /// <param name="identity"><see cref="IIdentity"/> supplies the <see cref="Name"/> and <see cref="AuthenticationType"/>.</param>
         /// <remarks><seealso cref="ClaimsIdentity(IIdentity, IEnumerable{Claim}, string, string, string)"/> for details on how internal values are set.</remarks>
-        public ClaimsIdentity(IIdentity identity)
-            : this(identity, (IEnumerable<Claim>)null, (string)null, (string)null, (string)null)
+        public ClaimsIdentity(IIdentity? identity)
+            : this(identity, (IEnumerable<Claim>?)null, (string?)null, (string?)null, (string?)null)
         {
         }
 
@@ -71,8 +71,8 @@ public ClaimsIdentity(IIdentity identity)
         /// <remarks>
         /// <remarks><seealso cref="ClaimsIdentity(IIdentity, IEnumerable{Claim}, string, string, string)"/> for details on how internal values are set.</remarks>
         /// </remarks>
-        public ClaimsIdentity(IEnumerable<Claim> claims)
-            : this((IIdentity)null, claims, (string)null, (string)null, (string)null)
+        public ClaimsIdentity(IEnumerable<Claim>? claims)
+            : this((IIdentity?)null, claims, (string?)null, (string?)null, (string?)null)
         {
         }
 
@@ -80,8 +80,8 @@ public ClaimsIdentity(IEnumerable<Claim> claims)
         /// Initializes an instance of <see cref="ClaimsIdentity"/>.
         /// </summary>
         /// <param name="authenticationType">The authentication method used to establish this identity.</param>
-        public ClaimsIdentity(string authenticationType)
-            : this((IIdentity)null, (IEnumerable<Claim>)null, authenticationType, (string)null, (string)null)
+        public ClaimsIdentity(string? authenticationType)
+            : this((IIdentity?)null, (IEnumerable<Claim>?)null, authenticationType, (string?)null, (string?)null)
         {
         }
 
@@ -91,8 +91,8 @@ public ClaimsIdentity(string authenticationType)
         /// <param name="claims"><see cref="IEnumerable{Claim}"/> associated with this instance.</param>
         /// <param name="authenticationType">The authentication method used to establish this identity.</param>
         /// <remarks><seealso cref="ClaimsIdentity(IIdentity, IEnumerable{Claim}, string, string, string)"/> for details on how internal values are set.</remarks>
-        public ClaimsIdentity(IEnumerable<Claim> claims, string authenticationType)
-            : this((IIdentity)null, claims, authenticationType, (string)null, (string)null)
+        public ClaimsIdentity(IEnumerable<Claim>? claims, string? authenticationType)
+            : this((IIdentity?)null, claims, authenticationType, (string?)null, (string?)null)
         {
         }
 
@@ -102,8 +102,8 @@ public ClaimsIdentity(IEnumerable<Claim> claims, string authenticationType)
         /// <param name="identity"><see cref="IIdentity"/> supplies the <see cref="Name"/> and <see cref="AuthenticationType"/>.</param>
         /// <param name="claims"><see cref="IEnumerable{Claim}"/> associated with this instance.</param>
         /// <remarks><seealso cref="ClaimsIdentity(IIdentity, IEnumerable{Claim}, string, string, string)"/> for details on how internal values are set.</remarks>
-        public ClaimsIdentity(IIdentity identity, IEnumerable<Claim> claims)
-            : this(identity, claims, (string)null, (string)null, (string)null)
+        public ClaimsIdentity(IIdentity? identity, IEnumerable<Claim>? claims)
+            : this(identity, claims, (string?)null, (string?)null, (string?)null)
         {
         }
 
@@ -114,8 +114,8 @@ public ClaimsIdentity(IIdentity identity, IEnumerable<Claim> claims)
         /// <param name="nameType">The <see cref="Claim.Type"/> used when obtaining the value of <see cref="ClaimsIdentity.Name"/>.</param>
         /// <param name="roleType">The <see cref="Claim.Type"/> used when performing logic for <see cref="ClaimsPrincipal.IsInRole"/>.</param>
         /// <remarks><seealso cref="ClaimsIdentity(IIdentity, IEnumerable{Claim}, string, string, string)"/> for details on how internal values are set.</remarks>
-        public ClaimsIdentity(string authenticationType, string nameType, string roleType)
-            : this((IIdentity)null, (IEnumerable<Claim>)null, authenticationType, nameType, roleType)
+        public ClaimsIdentity(string? authenticationType, string? nameType, string? roleType)
+            : this((IIdentity?)null, (IEnumerable<Claim>?)null, authenticationType, nameType, roleType)
         {
         }
 
@@ -127,8 +127,8 @@ public ClaimsIdentity(string authenticationType, string nameType, string roleTyp
         /// <param name="nameType">The <see cref="Claim.Type"/> used when obtaining the value of <see cref="ClaimsIdentity.Name"/>.</param>
         /// <param name="roleType">The <see cref="Claim.Type"/> used when performing logic for <see cref="ClaimsPrincipal.IsInRole"/>.</param>
         /// <remarks><seealso cref="ClaimsIdentity(IIdentity, IEnumerable{Claim}, string, string, string)"/> for details on how internal values are set.</remarks>
-        public ClaimsIdentity(IEnumerable<Claim> claims, string authenticationType, string nameType, string roleType)
-            : this((IIdentity)null, claims, authenticationType, nameType, roleType)
+        public ClaimsIdentity(IEnumerable<Claim>? claims, string? authenticationType, string? nameType, string? roleType)
+            : this((IIdentity?)null, claims, authenticationType, nameType, roleType)
         {
         }
 
@@ -146,9 +146,9 @@ public ClaimsIdentity(IEnumerable<Claim> claims, string authenticationType, stri
         /// <para>Any 'External' claims are ignored.</para>
         /// </remarks>
         /// <exception cref="InvalidOperationException">if 'identity' is a <see cref="ClaimsIdentity"/> and <see cref="ClaimsIdentity.Actor"/> results in a circular reference back to 'this'.</exception>
-        public ClaimsIdentity(IIdentity identity, IEnumerable<Claim> claims, string authenticationType, string nameType, string roleType)
+        public ClaimsIdentity(IIdentity? identity, IEnumerable<Claim>? claims, string? authenticationType, string? nameType, string? roleType)
         {
-            ClaimsIdentity claimsIdentity = identity as ClaimsIdentity;
+            ClaimsIdentity? claimsIdentity = identity as ClaimsIdentity;
 
             _authenticationType = (identity != null && string.IsNullOrEmpty(authenticationType)) ? identity.AuthenticationType : authenticationType;
             _nameClaimType = !string.IsNullOrEmpty(nameType) ? nameType : (claimsIdentity != null ? claimsIdentity._nameClaimType : DefaultNameClaimType);
@@ -255,7 +255,7 @@ protected ClaimsIdentity(SerializationInfo info)
         /// <summary>
         /// Gets the authentication type that can be used to determine how this <see cref="ClaimsIdentity"/> authenticated to an authority.
         /// </summary>
-        public virtual string AuthenticationType
+        public virtual string? AuthenticationType
         {
             get { return _authenticationType; }
         }
@@ -272,7 +272,7 @@ public virtual bool IsAuthenticated
         /// Gets or sets a <see cref="ClaimsIdentity"/> that was granted delegation rights.
         /// </summary>
         /// <exception cref="InvalidOperationException">if 'value' results in a circular reference back to 'this'.</exception>
-        public ClaimsIdentity Actor
+        public ClaimsIdentity? Actor
         {
             get { return _actor; }
             set
@@ -291,7 +291,7 @@ public ClaimsIdentity Actor
         /// <summary>
         /// Gets or sets a context that was used to create this <see cref="ClaimsIdentity"/>.
         /// </summary>
-        public object BootstrapContext
+        public object? BootstrapContext
         {
             get { return _bootstrapContext; }
             set { _bootstrapContext = value; }
@@ -301,7 +301,7 @@ public object BootstrapContext
         /// Gets the claims as <see cref="IEnumerable{Claim}"/>, associated with this <see cref="ClaimsIdentity"/>.
         /// </summary>
         /// <remarks>May contain nulls.</remarks>
-        public virtual IEnumerable<Claim> Claims
+        public virtual IEnumerable<Claim?> Claims
         {
             get
             {
@@ -314,14 +314,14 @@ public virtual IEnumerable<Claim> Claims
             }
         }
 
-        private IEnumerable<Claim> CombinedClaimsIterator()
+        private IEnumerable<Claim?> CombinedClaimsIterator()
         {
             for (int i = 0; i < _instanceClaims.Count; i++)
             {
                 yield return _instanceClaims[i];
             }
 
-            for (int j = 0; j < _externalClaims.Count; j++)
+            for (int j = 0; j < _externalClaims!.Count; j++)
             {
                 if (_externalClaims[j] != null)
                 {
@@ -336,7 +336,7 @@ private IEnumerable<Claim> CombinedClaimsIterator()
         /// <summary>
         /// Contains any additional data provided by a derived type, typically set when calling <see cref="WriteTo(BinaryWriter, byte[])"/>.
         /// </summary>
-        protected virtual byte[] CustomSerializationData
+        protected virtual byte[]? CustomSerializationData
         {
             get
             {
@@ -363,7 +363,7 @@ internal List<List<Claim>> ExternalClaims
         /// <summary>
         /// Gets or sets the label for this <see cref="ClaimsIdentity"/>
         /// </summary>
-        public string Label
+        public string? Label
         {
             get { return _label; }
             set { _label = value; }
@@ -373,12 +373,12 @@ public string Label
         /// Gets the Name of this <see cref="ClaimsIdentity"/>.
         /// </summary>
         /// <remarks>Calls <see cref="FindFirst(string)"/> where string == NameClaimType, if found, returns <see cref="Claim.Value"/> otherwise null.</remarks>
-        public virtual string Name
+        public virtual string? Name
         {
             // just an accessor for getting the name claim
             get
             {
-                Claim claim = FindFirst(_nameClaimType);
+                Claim? claim = FindFirst(_nameClaimType);
                 if (claim != null)
                 {
                     return claim.Value;
@@ -473,7 +473,7 @@ public virtual void AddClaims(IEnumerable<Claim> claims)
         /// <remarks> It is possible that a <see cref="Claim"/> returned from <see cref="Claims"/> cannot be removed. This would be the case for 'External' claims that are provided by reference.
         /// <para>object.ReferenceEquals is used to 'match'.</para>
         /// </remarks>
-        public virtual bool TryRemoveClaim(Claim claim)
+        public virtual bool TryRemoveClaim(Claim? claim)
         {
             if (claim == null)
             {
@@ -502,7 +502,7 @@ public virtual bool TryRemoveClaim(Claim claim)
         /// <para>object.ReferenceEquals is used to 'match'.</para>
         /// </remarks>
         /// <exception cref="InvalidOperationException">if 'claim' cannot be removed.</exception>
-        public virtual void RemoveClaim(Claim claim)
+        public virtual void RemoveClaim(Claim? claim)
         {
             if (!TryRemoveClaim(claim))
             {
@@ -515,9 +515,9 @@ public virtual void RemoveClaim(Claim claim)
         /// </summary>
         /// <param name="claims">a <see cref="IEnumerable{Claim}"/> to add to </param>
         /// <remarks>private only call from constructor, adds to internal list.</remarks>
-        private void SafeAddClaims(IEnumerable<Claim> claims)
+        private void SafeAddClaims(IEnumerable<Claim?> claims)
         {
-            foreach (Claim claim in claims)
+            foreach (Claim? claim in claims)
             {
                 if (claim == null)
                     continue;
@@ -537,7 +537,7 @@ private void SafeAddClaims(IEnumerable<Claim> claims)
         /// Adds claim to internal list. Calling Claim.Clone if Claim.Subject != this.
         /// </summary>
         /// <remarks>private only call from constructor, adds to internal list.</remarks>
-        private void SafeAddClaim(Claim claim)
+        private void SafeAddClaim(Claim? claim)
         {
             if (claim == null)
                 return;
@@ -558,14 +558,14 @@ private void SafeAddClaim(Claim claim)
         /// <param name="match">The function that performs the matching logic.</param>
         /// <returns>A <see cref="IEnumerable{Claim}"/> of matched claims.</returns>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual IEnumerable<Claim> FindAll(Predicate<Claim> match)
+        public virtual IEnumerable<Claim?> FindAll(Predicate<Claim?> match)
         {
             if (match == null)
             {
                 throw new ArgumentNullException(nameof(match));
             }
 
-            foreach (Claim claim in Claims)
+            foreach (Claim? claim in Claims)
             {
                 if (match(claim))
                 {
@@ -588,7 +588,7 @@ public virtual IEnumerable<Claim> FindAll(string type)
                 throw new ArgumentNullException(nameof(type));
             }
 
-            foreach (Claim claim in Claims)
+            foreach (Claim? claim in Claims)
             {
                 if (claim != null)
                 {
@@ -606,14 +606,14 @@ public virtual IEnumerable<Claim> FindAll(string type)
         /// <param name="match">The function that performs the matching logic.</param>
         /// <returns>A <see cref="Claim"/>, null if nothing matches.</returns>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual Claim FindFirst(Predicate<Claim> match)
+        public virtual Claim? FindFirst(Predicate<Claim?> match)
         {
             if (match == null)
             {
                 throw new ArgumentNullException(nameof(match));
             }
 
-            foreach (Claim claim in Claims)
+            foreach (Claim? claim in Claims)
             {
                 if (match(claim))
                 {
@@ -631,14 +631,14 @@ public virtual Claim FindFirst(Predicate<Claim> match)
         /// <returns>A <see cref="Claim"/>, null if nothing matches.</returns>
         /// <remarks>Comparison is: StringComparison.OrdinalIgnoreCase.</remarks>
         /// <exception cref="ArgumentNullException">if 'type' is null.</exception>
-        public virtual Claim FindFirst(string type)
+        public virtual Claim? FindFirst(string type)
         {
             if (type == null)
             {
                 throw new ArgumentNullException(nameof(type));
             }
 
-            foreach (Claim claim in Claims)
+            foreach (Claim? claim in Claims)
             {
                 if (claim != null)
                 {
@@ -658,14 +658,14 @@ public virtual Claim FindFirst(string type)
         /// <param name="match">The function that performs the matching logic.</param>
         /// <returns>true if a claim is found, false otherwise.</returns>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual bool HasClaim(Predicate<Claim> match)
+        public virtual bool HasClaim(Predicate<Claim?> match)
         {
             if (match == null)
             {
                 throw new ArgumentNullException(nameof(match));
             }
 
-            foreach (Claim claim in Claims)
+            foreach (Claim? claim in Claims)
             {
                 if (match(claim))
                 {
@@ -697,7 +697,7 @@ public virtual bool HasClaim(string type, string value)
                 throw new ArgumentNullException(nameof(value));
             }
 
-            foreach (Claim claim in Claims)
+            foreach (Claim? claim in Claims)
             {
                 if (claim != null
                         && string.Equals(claim.Type, type, StringComparison.OrdinalIgnoreCase)
@@ -825,7 +825,7 @@ public virtual void WriteTo(BinaryWriter writer)
         /// <param name="writer">the <see cref="BinaryWriter"/> to use for data storage.</param>
         /// <param name="userData">additional data provided by derived type.</param>
         /// <exception cref="ArgumentNullException">if 'writer' is null.</exception>
-        protected virtual void WriteTo(BinaryWriter writer, byte[] userData)
+        protected virtual void WriteTo(BinaryWriter writer, byte[]? userData)
         {
             if (writer == null)
             {
@@ -842,7 +842,7 @@ protected virtual void WriteTo(BinaryWriter writer, byte[] userData)
 
             if (_bootstrapContext != null)
             {
-                string rawData = _bootstrapContext as string;
+                string? rawData = _bootstrapContext as string;
                 if (rawData != null)
                 {
                     mask |= SerializationMask.BootstrapConext;
@@ -890,12 +890,12 @@ protected virtual void WriteTo(BinaryWriter writer, byte[] userData)
             writer.Write(numberOfPropertiesWritten);
             if ((mask & SerializationMask.AuthenticationType) == SerializationMask.AuthenticationType)
             {
-                writer.Write(_authenticationType);
+                writer.Write(_authenticationType!);
             }
 
             if ((mask & SerializationMask.BootstrapConext) == SerializationMask.BootstrapConext)
             {
-                writer.Write(_bootstrapContext as string);
+                writer.Write((_bootstrapContext as string)!);
             }
 
             if ((mask & SerializationMask.NameClaimType) == SerializationMask.NameClaimType)
@@ -910,7 +910,7 @@ protected virtual void WriteTo(BinaryWriter writer, byte[] userData)
 
             if ((mask & SerializationMask.HasLabel) == SerializationMask.HasLabel)
             {
-                writer.Write(_label);
+                writer.Write(_label!);
             }
 
             if ((mask & SerializationMask.HasClaims) == SerializationMask.HasClaims)
@@ -918,18 +918,18 @@ protected virtual void WriteTo(BinaryWriter writer, byte[] userData)
                 writer.Write(_instanceClaims.Count);
                 foreach (var claim in _instanceClaims)
                 {
-                    claim.WriteTo(writer);
+                    claim!.WriteTo(writer);
                 }
             }
 
             if ((mask & SerializationMask.Actor) == SerializationMask.Actor)
             {
-                _actor.WriteTo(writer);
+                _actor!.WriteTo(writer);
             }
 
             if ((mask & SerializationMask.UserData) == SerializationMask.UserData)
             {
-                writer.Write(userData.Length);
+                writer.Write(userData!.Length);
                 writer.Write(userData);
             }
 
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs
index 6bc0b19f13cbf3..db48fec299d7ad 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs
@@ -22,9 +22,9 @@ private enum SerializationMask
         }
 
         private readonly List<ClaimsIdentity> _identities = new List<ClaimsIdentity>();
-        private readonly byte[] _userSerializationData;
+        private readonly byte[]? _userSerializationData;
 
-        private static Func<IEnumerable<ClaimsIdentity>, ClaimsIdentity> s_identitySelector = SelectPrimaryIdentity;
+        private static Func<IEnumerable<ClaimsIdentity>, ClaimsIdentity?> s_identitySelector = SelectPrimaryIdentity;
         private static Func<ClaimsPrincipal> s_principalSelector = ClaimsPrincipalSelector;
 
         protected ClaimsPrincipal(SerializationInfo info, StreamingContext context)
@@ -35,7 +35,7 @@ protected ClaimsPrincipal(SerializationInfo info, StreamingContext context)
         /// <summary>
         /// This method iterates through the collection of ClaimsIdentities and chooses an identity as the primary.
         /// </summary>
-        private static ClaimsIdentity SelectPrimaryIdentity(IEnumerable<ClaimsIdentity> identities)
+        private static ClaimsIdentity? SelectPrimaryIdentity(IEnumerable<ClaimsIdentity> identities)
         {
             if (identities == null)
             {
@@ -53,7 +53,7 @@ private static ClaimsIdentity SelectPrimaryIdentity(IEnumerable<ClaimsIdentity>
             return null;
         }
 
-        public static Func<IEnumerable<ClaimsIdentity>, ClaimsIdentity> PrimaryIdentitySelector
+        public static Func<IEnumerable<ClaimsIdentity>, ClaimsIdentity?> PrimaryIdentitySelector
         {
             get
             {
@@ -111,7 +111,7 @@ public ClaimsPrincipal(IIdentity identity)
                 throw new ArgumentNullException(nameof(identity));
             }
 
-            ClaimsIdentity ci = identity as ClaimsIdentity;
+            ClaimsIdentity? ci = identity as ClaimsIdentity;
             if (ci != null)
             {
                 _identities.Add(ci);
@@ -138,7 +138,7 @@ public ClaimsPrincipal(IPrincipal principal)
             // If IPrincipal is a ClaimsPrincipal add all of the identities
             // If IPrincipal is not a ClaimsPrincipal, create a new identity from IPrincipal.Identity
             //
-            ClaimsPrincipal cp = principal as ClaimsPrincipal;
+            ClaimsPrincipal? cp = principal as ClaimsPrincipal;
             if (null == cp)
             {
                 _identities.Add(new ClaimsIdentity(principal.Identity));
@@ -225,13 +225,13 @@ public virtual void AddIdentities(IEnumerable<ClaimsIdentity> identities)
         /// <summary>
         /// Gets the claims as <see cref="IEnumerable{Claim}"/>, associated with this <see cref="ClaimsPrincipal"/> by enumerating all <see cref="Identities"/>.
         /// </summary>
-        public virtual IEnumerable<Claim> Claims
+        public virtual IEnumerable<Claim?> Claims
         {
             get
             {
                 foreach (ClaimsIdentity identity in Identities)
                 {
-                    foreach (Claim claim in identity.Claims)
+                    foreach (Claim? claim in identity.Claims)
                     {
                         yield return claim;
                     }
@@ -242,7 +242,7 @@ public virtual IEnumerable<Claim> Claims
         /// <summary>
         /// Contains any additional data provided by derived type, typically set when calling <see cref="WriteTo(BinaryWriter, byte[])"/>.
         /// </summary>
-        protected virtual byte[] CustomSerializationData
+        protected virtual byte[]? CustomSerializationData
         {
             get
             {
@@ -277,7 +277,7 @@ protected virtual ClaimsIdentity CreateClaimsIdentity(BinaryReader reader)
         /// <summary>
         /// Returns the Current Principal by calling a delegate.  Users may specify the delegate.
         /// </summary>
-        public static ClaimsPrincipal Current
+        public static ClaimsPrincipal? Current
         {
             // just accesses the current selected principal selector, doesn't set
             get
@@ -298,7 +298,7 @@ public static ClaimsPrincipal Current
         /// <returns>A <see cref="IEnumerable{Claim}"/> of matched claims.</returns>
         /// <remarks>Each <see cref="ClaimsIdentity"/> is called. <seealso cref="ClaimsIdentity.FindAll(string)"/>.</remarks>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual IEnumerable<Claim> FindAll(Predicate<Claim> match)
+        public virtual IEnumerable<Claim?> FindAll(Predicate<Claim?> match)
         {
             if (match == null)
             {
@@ -309,7 +309,7 @@ public virtual IEnumerable<Claim> FindAll(Predicate<Claim> match)
             {
                 if (identity != null)
                 {
-                    foreach (Claim claim in identity.FindAll(match))
+                    foreach (Claim? claim in identity.FindAll(match))
                     {
                         yield return claim;
                     }
@@ -350,14 +350,14 @@ public virtual IEnumerable<Claim> FindAll(string type)
         /// <returns>A <see cref="Claim"/>, null if nothing matches.</returns>
         /// <remarks>Each <see cref="ClaimsIdentity"/> is called. <seealso cref="ClaimsIdentity.FindFirst(string)"/>.</remarks>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual Claim FindFirst(Predicate<Claim> match)
+        public virtual Claim? FindFirst(Predicate<Claim?> match)
         {
             if (match == null)
             {
                 throw new ArgumentNullException(nameof(match));
             }
 
-            Claim claim = null;
+            Claim? claim = null;
 
             foreach (ClaimsIdentity identity in Identities)
             {
@@ -381,14 +381,14 @@ public virtual Claim FindFirst(Predicate<Claim> match)
         /// <returns>A <see cref="Claim"/>, null if nothing matches.</returns>
         /// <remarks>Each <see cref="ClaimsIdentity"/> is called. <seealso cref="ClaimsIdentity.FindFirst(Predicate{Claim})"/>.</remarks>
         /// <exception cref="ArgumentNullException">if 'type' is null.</exception>
-        public virtual Claim FindFirst(string type)
+        public virtual Claim? FindFirst(string type)
         {
             if (type == null)
             {
                 throw new ArgumentNullException(nameof(type));
             }
 
-            Claim claim = null;
+            Claim? claim = null;
 
             for (int i = 0; i < _identities.Count; i++)
             {
@@ -412,7 +412,7 @@ public virtual Claim FindFirst(string type)
         /// <returns>true if a claim is found, false otherwise.</returns>
         /// <remarks>Each <see cref="ClaimsIdentity"/> is called. <seealso cref="ClaimsIdentity.HasClaim(string, string)"/>.</remarks>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual bool HasClaim(Predicate<Claim> match)
+        public virtual bool HasClaim(Predicate<Claim?> match)
         {
             if (match == null)
             {
@@ -482,7 +482,7 @@ public virtual IEnumerable<ClaimsIdentity> Identities
         /// <summary>
         /// Gets the identity of the current principal.
         /// </summary>
-        public virtual System.Security.Principal.IIdentity Identity
+        public virtual System.Security.Principal.IIdentity? Identity
         {
             get
             {
@@ -535,7 +535,7 @@ public virtual void WriteTo(BinaryWriter writer)
         /// <param name="writer">the <see cref="BinaryWriter"/> to use for data storage.</param>
         /// <param name="userData">additional data provided by derived type.</param>
         /// <exception cref="ArgumentNullException">if 'writer' is null.</exception>
-        protected virtual void WriteTo(BinaryWriter writer, byte[] userData)
+        protected virtual void WriteTo(BinaryWriter writer, byte[]? userData)
         {
             if (writer == null)
             {
@@ -569,7 +569,7 @@ protected virtual void WriteTo(BinaryWriter writer, byte[] userData)
 
             if ((mask & SerializationMask.UserData) == SerializationMask.UserData)
             {
-                writer.Write(userData.Length);
+                writer.Write(userData!.Length);
                 writer.Write(userData);
             }
 
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
index 1fb721b228c505..40d6a2345b2879 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
@@ -9,8 +9,8 @@ namespace System.Security.Principal
 {
     public class GenericIdentity : ClaimsIdentity
     {
-        private readonly string m_name;
-        private readonly string m_type;
+        private readonly string m_name = null!;  // Init-ed in parameterized constructors
+        private readonly string m_type = null!;
 
         public GenericIdentity(string name)
         {
@@ -56,7 +56,7 @@ public override ClaimsIdentity Clone()
             return new GenericIdentity(this);
         }
 
-        public override IEnumerable<Claim> Claims
+        public override IEnumerable<Claim?> Claims
         {
             get
             {
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericPrincipal.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericPrincipal.cs
index aac4c43c5b68d7..b20959418b3640 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericPrincipal.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericPrincipal.cs
@@ -10,9 +10,9 @@ namespace System.Security.Principal
     public class GenericPrincipal : ClaimsPrincipal
     {
         private readonly IIdentity m_identity;
-        private readonly string[] m_roles;
+        private readonly string[]? m_roles;
 
-        public GenericPrincipal(IIdentity identity, string[] roles)
+        public GenericPrincipal(IIdentity identity, string[]? roles)
         {
             if (identity == null)
                 throw new ArgumentNullException(nameof(identity));
@@ -33,9 +33,9 @@ public GenericPrincipal(IIdentity identity, string[] roles)
         /// <summary>
         /// helper method to add roles
         /// </summary>
-        private void AddIdentityWithRoles(IIdentity identity, string[] roles)
+        private void AddIdentityWithRoles(IIdentity identity, string[]? roles)
         {
-            ClaimsIdentity claimsIdentity = identity as ClaimsIdentity;
+            ClaimsIdentity? claimsIdentity = identity as ClaimsIdentity;
 
             if (claimsIdentity != null)
             {
@@ -70,7 +70,7 @@ public override IIdentity Identity
             get { return m_identity; }
         }
 
-        public override bool IsInRole(string role)
+        public override bool IsInRole(string? role)
         {
             if (role == null || m_roles == null)
                 return false;

From a972883f073d67106a1cd19155b40ba163390708 Mon Sep 17 00:00:00 2001
From: Buyaa Namnan <bunamnan@microsoft.com>
Date: Tue, 7 Jan 2020 16:30:49 -0800
Subject: [PATCH 2/6] Some update

---
 .../ref/System.Security.Claims.cs             | 14 +++++-----
 .../System/Security/Claims/ClaimsIdentity.cs  | 28 +++++++++----------
 .../System/Security/Claims/ClaimsPrincipal.cs | 12 ++++----
 .../System/Security/Claims/GenericIdentity.cs |  2 +-
 4 files changed, 28 insertions(+), 28 deletions(-)

diff --git a/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs b/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs
index 781c9899845d7c..17fe4f57a8fe65 100644
--- a/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs
+++ b/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs
@@ -64,9 +64,9 @@ public virtual void AddClaim(System.Security.Claims.Claim claim) { }
         public virtual void AddClaims(System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> claims) { }
         public virtual System.Security.Claims.ClaimsIdentity Clone() { throw null; }
         protected virtual System.Security.Claims.Claim CreateClaim(System.IO.BinaryReader reader) { throw null; }
-        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> FindAll(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
+        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> FindAll(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
         public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> FindAll(string type) { throw null; }
-        public virtual System.Security.Claims.Claim? FindFirst(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
+        public virtual System.Security.Claims.Claim? FindFirst(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
         public virtual System.Security.Claims.Claim? FindFirst(string type) { throw null; }
         protected virtual void GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         public virtual bool HasClaim(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
@@ -84,7 +84,7 @@ public ClaimsPrincipal(System.IO.BinaryReader reader) { }
         protected ClaimsPrincipal(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         public ClaimsPrincipal(System.Security.Principal.IIdentity identity) { }
         public ClaimsPrincipal(System.Security.Principal.IPrincipal principal) { }
-        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> Claims { get { throw null; } }
+        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> Claims { get { throw null; } }
         public static System.Func<System.Security.Claims.ClaimsPrincipal> ClaimsPrincipalSelector { get { throw null; } set { } }
         public static System.Security.Claims.ClaimsPrincipal? Current { get { throw null; } }
         protected virtual byte[]? CustomSerializationData { get { throw null; } }
@@ -95,12 +95,12 @@ public virtual void AddIdentities(System.Collections.Generic.IEnumerable<System.
         public virtual void AddIdentity(System.Security.Claims.ClaimsIdentity identity) { }
         public virtual System.Security.Claims.ClaimsPrincipal Clone() { throw null; }
         protected virtual System.Security.Claims.ClaimsIdentity CreateClaimsIdentity(System.IO.BinaryReader reader) { throw null; }
-        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> FindAll(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
+        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> FindAll(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
         public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> FindAll(string type) { throw null; }
-        public virtual System.Security.Claims.Claim? FindFirst(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
+        public virtual System.Security.Claims.Claim? FindFirst(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
         public virtual System.Security.Claims.Claim? FindFirst(string type) { throw null; }
         protected virtual void GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
-        public virtual bool HasClaim(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
+        public virtual bool HasClaim(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
         public virtual bool HasClaim(string type, string value) { throw null; }
         public virtual bool IsInRole(string role) { throw null; }
         public virtual void WriteTo(System.IO.BinaryWriter writer) { }
@@ -202,7 +202,7 @@ protected GenericIdentity(System.Security.Principal.GenericIdentity identity) {
         public GenericIdentity(string name) { }
         public GenericIdentity(string name, string type) { }
         public override string AuthenticationType { get { throw null; } }
-        public override System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> Claims { get { throw null; } }
+        public override System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> Claims { get { throw null; } }
         public override bool IsAuthenticated { get { throw null; } }
         public override string Name { get { throw null; } }
         public override System.Security.Claims.ClaimsIdentity Clone() { throw null; }
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
index 4924e51df48f9e..d052dd636943df 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
@@ -33,7 +33,7 @@ private enum SerializationMask
         private object? _bootstrapContext;
         private List<List<Claim>>? _externalClaims;
         private string? _label;
-        private readonly List<Claim?> _instanceClaims = new List<Claim?>();
+        private readonly List<Claim> _instanceClaims = new List<Claim>();
         private string _nameClaimType = DefaultNameClaimType;
         private string _roleClaimType = DefaultRoleClaimType;
 
@@ -301,7 +301,7 @@ public object? BootstrapContext
         /// Gets the claims as <see cref="IEnumerable{Claim}"/>, associated with this <see cref="ClaimsIdentity"/>.
         /// </summary>
         /// <remarks>May contain nulls.</remarks>
-        public virtual IEnumerable<Claim?> Claims
+        public virtual IEnumerable<Claim> Claims
         {
             get
             {
@@ -314,7 +314,7 @@ public virtual IEnumerable<Claim?> Claims
             }
         }
 
-        private IEnumerable<Claim?> CombinedClaimsIterator()
+        private IEnumerable<Claim> CombinedClaimsIterator()
         {
             for (int i = 0; i < _instanceClaims.Count; i++)
             {
@@ -441,14 +441,14 @@ public virtual void AddClaim(Claim claim)
         /// <param name="claims">Enumeration of claims to add.</param>
         /// <remarks>Each claim is examined and if <see cref="Claim.Subject"/> != this, then Claim.Clone(this) is called before the claim is added.</remarks>
         /// <exception cref="ArgumentNullException">if 'claims' is null.</exception>
-        public virtual void AddClaims(IEnumerable<Claim> claims)
+        public virtual void AddClaims(IEnumerable<Claim?> claims)
         {
             if (claims == null)
             {
                 throw new ArgumentNullException(nameof(claims));
             }
 
-            foreach (Claim claim in claims)
+            foreach (Claim? claim in claims)
             {
                 if (claim == null)
                 {
@@ -558,14 +558,14 @@ private void SafeAddClaim(Claim? claim)
         /// <param name="match">The function that performs the matching logic.</param>
         /// <returns>A <see cref="IEnumerable{Claim}"/> of matched claims.</returns>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual IEnumerable<Claim?> FindAll(Predicate<Claim?> match)
+        public virtual IEnumerable<Claim> FindAll(Predicate<Claim> match)
         {
             if (match == null)
             {
                 throw new ArgumentNullException(nameof(match));
             }
 
-            foreach (Claim? claim in Claims)
+            foreach (Claim claim in Claims)
             {
                 if (match(claim))
                 {
@@ -588,7 +588,7 @@ public virtual IEnumerable<Claim> FindAll(string type)
                 throw new ArgumentNullException(nameof(type));
             }
 
-            foreach (Claim? claim in Claims)
+            foreach (Claim claim in Claims)
             {
                 if (claim != null)
                 {
@@ -606,14 +606,14 @@ public virtual IEnumerable<Claim> FindAll(string type)
         /// <param name="match">The function that performs the matching logic.</param>
         /// <returns>A <see cref="Claim"/>, null if nothing matches.</returns>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual Claim? FindFirst(Predicate<Claim?> match)
+        public virtual Claim? FindFirst(Predicate<Claim> match)
         {
             if (match == null)
             {
                 throw new ArgumentNullException(nameof(match));
             }
 
-            foreach (Claim? claim in Claims)
+            foreach (Claim claim in Claims)
             {
                 if (match(claim))
                 {
@@ -638,7 +638,7 @@ public virtual IEnumerable<Claim> FindAll(string type)
                 throw new ArgumentNullException(nameof(type));
             }
 
-            foreach (Claim? claim in Claims)
+            foreach (Claim claim in Claims)
             {
                 if (claim != null)
                 {
@@ -658,14 +658,14 @@ public virtual IEnumerable<Claim> FindAll(string type)
         /// <param name="match">The function that performs the matching logic.</param>
         /// <returns>true if a claim is found, false otherwise.</returns>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual bool HasClaim(Predicate<Claim?> match)
+        public virtual bool HasClaim(Predicate<Claim> match)
         {
             if (match == null)
             {
                 throw new ArgumentNullException(nameof(match));
             }
 
-            foreach (Claim? claim in Claims)
+            foreach (Claim claim in Claims)
             {
                 if (match(claim))
                 {
@@ -697,7 +697,7 @@ public virtual bool HasClaim(string type, string value)
                 throw new ArgumentNullException(nameof(value));
             }
 
-            foreach (Claim? claim in Claims)
+            foreach (Claim claim in Claims)
             {
                 if (claim != null
                         && string.Equals(claim.Type, type, StringComparison.OrdinalIgnoreCase)
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs
index db48fec299d7ad..abeff195d78b9d 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs
@@ -225,13 +225,13 @@ public virtual void AddIdentities(IEnumerable<ClaimsIdentity> identities)
         /// <summary>
         /// Gets the claims as <see cref="IEnumerable{Claim}"/>, associated with this <see cref="ClaimsPrincipal"/> by enumerating all <see cref="Identities"/>.
         /// </summary>
-        public virtual IEnumerable<Claim?> Claims
+        public virtual IEnumerable<Claim> Claims
         {
             get
             {
                 foreach (ClaimsIdentity identity in Identities)
                 {
-                    foreach (Claim? claim in identity.Claims)
+                    foreach (Claim claim in identity.Claims)
                     {
                         yield return claim;
                     }
@@ -298,7 +298,7 @@ public static ClaimsPrincipal? Current
         /// <returns>A <see cref="IEnumerable{Claim}"/> of matched claims.</returns>
         /// <remarks>Each <see cref="ClaimsIdentity"/> is called. <seealso cref="ClaimsIdentity.FindAll(string)"/>.</remarks>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual IEnumerable<Claim?> FindAll(Predicate<Claim?> match)
+        public virtual IEnumerable<Claim> FindAll(Predicate<Claim> match)
         {
             if (match == null)
             {
@@ -309,7 +309,7 @@ public static ClaimsPrincipal? Current
             {
                 if (identity != null)
                 {
-                    foreach (Claim? claim in identity.FindAll(match))
+                    foreach (Claim claim in identity.FindAll(match))
                     {
                         yield return claim;
                     }
@@ -350,7 +350,7 @@ public virtual IEnumerable<Claim> FindAll(string type)
         /// <returns>A <see cref="Claim"/>, null if nothing matches.</returns>
         /// <remarks>Each <see cref="ClaimsIdentity"/> is called. <seealso cref="ClaimsIdentity.FindFirst(string)"/>.</remarks>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual Claim? FindFirst(Predicate<Claim?> match)
+        public virtual Claim? FindFirst(Predicate<Claim> match)
         {
             if (match == null)
             {
@@ -412,7 +412,7 @@ public virtual IEnumerable<Claim> FindAll(string type)
         /// <returns>true if a claim is found, false otherwise.</returns>
         /// <remarks>Each <see cref="ClaimsIdentity"/> is called. <seealso cref="ClaimsIdentity.HasClaim(string, string)"/>.</remarks>
         /// <exception cref="ArgumentNullException">if 'match' is null.</exception>
-        public virtual bool HasClaim(Predicate<Claim?> match)
+        public virtual bool HasClaim(Predicate<Claim> match)
         {
             if (match == null)
             {
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
index 40d6a2345b2879..3bc44c3514c9a0 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
@@ -56,7 +56,7 @@ public override ClaimsIdentity Clone()
             return new GenericIdentity(this);
         }
 
-        public override IEnumerable<Claim?> Claims
+        public override IEnumerable<Claim> Claims
         {
             get
             {

From f67362e6957bfd1dd670b06c316f6a64ec89f0c8 Mon Sep 17 00:00:00 2001
From: Buyaa Namnan <bunamnan@microsoft.com>
Date: Tue, 7 Jan 2020 16:35:43 -0800
Subject: [PATCH 3/6] Ref update

---
 .../System.Security.Claims/ref/System.Security.Claims.cs    | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs b/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs
index 17fe4f57a8fe65..03cc48db5077e8 100644
--- a/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs
+++ b/src/libraries/System.Security.Claims/ref/System.Security.Claims.cs
@@ -53,7 +53,7 @@ public ClaimsIdentity(string? authenticationType, string? nameType, string? role
         public System.Security.Claims.ClaimsIdentity? Actor { get { throw null; } set { } }
         public virtual string? AuthenticationType { get { throw null; } }
         public object? BootstrapContext { get { throw null; } set { } }
-        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> Claims { get { throw null; } }
+        public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> Claims { get { throw null; } }
         protected virtual byte[]? CustomSerializationData { get { throw null; } }
         public virtual bool IsAuthenticated { get { throw null; } }
         public string? Label { get { throw null; } set { } }
@@ -61,7 +61,7 @@ public ClaimsIdentity(string? authenticationType, string? nameType, string? role
         public string NameClaimType { get { throw null; } }
         public string RoleClaimType { get { throw null; } }
         public virtual void AddClaim(System.Security.Claims.Claim claim) { }
-        public virtual void AddClaims(System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> claims) { }
+        public virtual void AddClaims(System.Collections.Generic.IEnumerable<System.Security.Claims.Claim?> claims) { }
         public virtual System.Security.Claims.ClaimsIdentity Clone() { throw null; }
         protected virtual System.Security.Claims.Claim CreateClaim(System.IO.BinaryReader reader) { throw null; }
         public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> FindAll(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
@@ -69,7 +69,7 @@ public virtual void AddClaims(System.Collections.Generic.IEnumerable<System.Secu
         public virtual System.Security.Claims.Claim? FindFirst(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
         public virtual System.Security.Claims.Claim? FindFirst(string type) { throw null; }
         protected virtual void GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
-        public virtual bool HasClaim(System.Predicate<System.Security.Claims.Claim?> match) { throw null; }
+        public virtual bool HasClaim(System.Predicate<System.Security.Claims.Claim> match) { throw null; }
         public virtual bool HasClaim(string type, string value) { throw null; }
         public virtual void RemoveClaim(System.Security.Claims.Claim? claim) { }
         public virtual bool TryRemoveClaim(System.Security.Claims.Claim? claim) { throw null; }

From 606026ba81ed4e857a13a0d35d70f74f2a0139ff Mon Sep 17 00:00:00 2001
From: Buyaa Namnan <bunamnan@microsoft.com>
Date: Wed, 8 Jan 2020 15:30:54 -0800
Subject: [PATCH 4/6] Addressing feedback

---
 .../src/System/Security/Claims/GenericIdentity.cs               | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
index 3bc44c3514c9a0..a3c161cfd56bd6 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
@@ -9,7 +9,7 @@ namespace System.Security.Principal
 {
     public class GenericIdentity : ClaimsIdentity
     {
-        private readonly string m_name = null!;  // Init-ed in parameterized constructors
+        private readonly string m_name = null!;  // Initialized in parameterized constructors
         private readonly string m_type = null!;
 
         public GenericIdentity(string name)

From 148638ca5be8acbc865ecefb988be990bf85bc7e Mon Sep 17 00:00:00 2001
From: Buyaa Namnan <bunamnan@microsoft.com>
Date: Thu, 9 Jan 2020 15:43:22 -0800
Subject: [PATCH 5/6] as => is updates

---
 .../src/System/Security/Claims/ClaimsIdentity.cs              | 3 +--
 .../src/System/Security/Claims/ClaimsPrincipal.cs             | 3 +--
 .../src/System/Security/Claims/GenericPrincipal.cs            | 4 +---
 3 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
index d052dd636943df..346a34bd1e2655 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
@@ -842,8 +842,7 @@ protected virtual void WriteTo(BinaryWriter writer, byte[]? userData)
 
             if (_bootstrapContext != null)
             {
-                string? rawData = _bootstrapContext as string;
-                if (rawData != null)
+                if (_bootstrapContext is string rawData)
                 {
                     mask |= SerializationMask.BootstrapConext;
                     numberOfPropertiesWritten++;
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs
index abeff195d78b9d..bc7dab0a78ee22 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs
@@ -111,8 +111,7 @@ public ClaimsPrincipal(IIdentity identity)
                 throw new ArgumentNullException(nameof(identity));
             }
 
-            ClaimsIdentity? ci = identity as ClaimsIdentity;
-            if (ci != null)
+            if (identity is ClaimsIdentity ci)
             {
                 _identities.Add(ci);
             }
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericPrincipal.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericPrincipal.cs
index b20959418b3640..8b4c9a56840926 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericPrincipal.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericPrincipal.cs
@@ -35,9 +35,7 @@ public GenericPrincipal(IIdentity identity, string[]? roles)
         /// </summary>
         private void AddIdentityWithRoles(IIdentity identity, string[]? roles)
         {
-            ClaimsIdentity? claimsIdentity = identity as ClaimsIdentity;
-
-            if (claimsIdentity != null)
+            if (identity is ClaimsIdentity claimsIdentity)
             {
                 claimsIdentity = claimsIdentity.Clone();
             }

From d0733285c729d68ee235c1658f5de52d4020119c Mon Sep 17 00:00:00 2001
From: Buyaa Namnan <bunamnan@microsoft.com>
Date: Fri, 10 Jan 2020 15:30:48 -0800
Subject: [PATCH 6/6] Applying feedback

---
 .../src/System/Security/Claims/Claim.cs           | 15 ++++++++-------
 .../src/System/Security/Claims/ClaimsIdentity.cs  |  4 ++--
 .../src/System/Security/Claims/GenericIdentity.cs |  9 ++-------
 3 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/Claim.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/Claim.cs
index 7a64b9dcf4d130..d48914daf00cdc 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/Claim.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/Claim.cs
@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 
 namespace System.Security.Claims
@@ -31,7 +32,7 @@ private enum SerializationMask
 
         private readonly string _issuer;
         private readonly string _originalIssuer;
-        private Dictionary<string, string?>? _properties;
+        private Dictionary<string, string>? _properties;
 
         private readonly ClaimsIdentity? _subject;
         private readonly string _type;
@@ -272,8 +273,8 @@ internal Claim(string type, string value, string? valueType, string? issuer, str
 
             if (propertyKey != null)
             {
-                _properties = new Dictionary<string, string?>();
-                _properties[propertyKey] = propertyValue;
+                _properties = new Dictionary<string, string>();
+                _properties[propertyKey] = propertyValue!;
             }
         }
 
@@ -308,7 +309,7 @@ protected Claim(Claim other, ClaimsIdentity? subject)
             _valueType = other._valueType;
             if (other._properties != null)
             {
-                _properties = new Dictionary<string, string?>(other._properties);
+                _properties = new Dictionary<string, string>(other._properties);
             }
 
             if (other._userSerializationData != null)
@@ -352,13 +353,13 @@ public string OriginalIssuer
         /// <summary>
         /// Gets the collection of Properties associated with the <see cref="Claim"/>.
         /// </summary>
-        public IDictionary<string, string?> Properties
+        public IDictionary<string, string> Properties
         {
             get
             {
                 if (_properties == null)
                 {
-                    _properties = new Dictionary<string, string?>();
+                    _properties = new Dictionary<string, string>();
                 }
                 return _properties;
             }
@@ -518,7 +519,7 @@ protected virtual void WriteTo(BinaryWriter writer, byte[]? userData)
                 foreach (var kvp in _properties)
                 {
                     writer.Write(kvp.Key);
-                    writer.Write(kvp.Value!);
+                    writer.Write(kvp.Value);
                 }
             }
 
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
index 346a34bd1e2655..d1507e2314835e 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsIdentity.cs
@@ -894,7 +894,7 @@ protected virtual void WriteTo(BinaryWriter writer, byte[]? userData)
 
             if ((mask & SerializationMask.BootstrapConext) == SerializationMask.BootstrapConext)
             {
-                writer.Write((_bootstrapContext as string)!);
+                writer.Write((string)_bootstrapContext!);
             }
 
             if ((mask & SerializationMask.NameClaimType) == SerializationMask.NameClaimType)
@@ -917,7 +917,7 @@ protected virtual void WriteTo(BinaryWriter writer, byte[]? userData)
                 writer.Write(_instanceClaims.Count);
                 foreach (var claim in _instanceClaims)
                 {
-                    claim!.WriteTo(writer);
+                    claim.WriteTo(writer);
                 }
             }
 
diff --git a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
index a3c161cfd56bd6..4f0cc83fecfd6d 100644
--- a/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
+++ b/src/libraries/System.Security.Claims/src/System/Security/Claims/GenericIdentity.cs
@@ -9,8 +9,8 @@ namespace System.Security.Principal
 {
     public class GenericIdentity : ClaimsIdentity
     {
-        private readonly string m_name = null!;  // Initialized in parameterized constructors
-        private readonly string m_type = null!;
+        private readonly string m_name;
+        private readonly string m_type;
 
         public GenericIdentity(string name)
         {
@@ -36,11 +36,6 @@ public GenericIdentity(string name, string type)
             AddNameClaim();
         }
 
-        private GenericIdentity()
-            : base()
-        { }
-
-
         protected GenericIdentity(GenericIdentity identity)
             : base(identity)
         {