Add NRT annotations required for the new Newtonsoft.Json version

src/EFCore.Cosmos/Storage/Internal/ByteArrayConverter.cs

@@ -51,7 +51,7 @@ public override void WriteJson(
     public override object ReadJson(
         JsonReader reader,
         Type objectType,
-        object existingValue,
+        object? existingValue,
         JsonSerializer serializer)
     {
         if (reader.TokenType != JsonToken.StartArray)

src/EFCore.Cosmos/Storage/Internal/CosmosClientWrapper.cs

@@ -359,7 +359,7 @@ private static async Task<bool> CreateItemOnceAsync(
             response.Diagnostics.GetClientElapsedTime(),
             response.Headers.RequestCharge,
             response.Headers.ActivityId,
-            parameters.Document["id"].ToString(),
+            parameters.Document["id"]!.ToString(),
             parameters.ContainerId,
             partitionKeyValue);
 

src/EFCore.Cosmos/Storage/Internal/CosmosDatabaseWrapper.cs

@@ -246,7 +246,7 @@ private bool Save(IUpdateEntry entry)
                     if (propertyName != null)
                     {
                         document[propertyName] =
-                            JToken.FromObject(entityType.GetDiscriminatorValue(), CosmosClientWrapper.Serializer);
+                            JToken.FromObject(entityType.GetDiscriminatorValue()!, CosmosClientWrapper.Serializer);
                     }
                 }
 
@@ -377,7 +377,7 @@ private Task<bool> SaveAsync(IUpdateEntry entry, CancellationToken cancellationT
                     if (propertyName != null)
                     {
                         document[propertyName] =
-                            JToken.FromObject(entityType.GetDiscriminatorValue(), CosmosClientWrapper.Serializer);
+                            JToken.FromObject(entityType.GetDiscriminatorValue()!, CosmosClientWrapper.Serializer);
                     }
                 }
 

src/EFCore.Cosmos/Storage/Internal/JsonCosmosSerializer.cs

@@ -28,7 +28,7 @@ public override T FromStream<T>(Stream stream)
 
             using var streamReader = new StreamReader(stream);
             using var jsonTextReader = new JsonTextReader(streamReader);
-            return GetSerializer().Deserialize<T>(jsonTextReader);
+            return GetSerializer().Deserialize<T>(jsonTextReader)!;
         }
     }