diff --git a/modules/swagger-codegen/src/main/resources/nancyfx/api.mustache b/modules/swagger-codegen/src/main/resources/nancyfx/api.mustache
index 1e66c83c769..b4213ff2056 100644
--- a/modules/swagger-codegen/src/main/resources/nancyfx/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/nancyfx/api.mustache
@@ -30,7 +30,7 @@ namespace {{packageName}}.{{packageContext}}.Modules
                 {{/hasMore}}{{/isBodyParam}}{{/allParams}}{{#allParams}}{{#required}}
                 Preconditions.IsNotNull({{paramName}}, "Required parameter: '{{paramName}}' is missing at '{{operationId}}'");
                 {{/required}}{{/allParams}}
-                {{#returnType}}return {{/returnType}}service.{{operationId}}(Context{{#allParams.0}}, {{/allParams.0}}{{#allParams}}{{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}});{{^returnType}}
+                {{#returnType}}return {{/returnType}}service.{{operationId}}(Context{{#allParams.0}}, {{/allParams.0}}{{#allParams}}{{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}}){{#returnType}}{{#isListContainer}}.ToArray(){{/isListContainer}}{{/returnType}};{{^returnType}}
                 return new Response { ContentType = "{{produces.0.mediaType}}"};{{/returnType}}
             };
 {{/operation}}
diff --git a/modules/swagger-codegen/src/main/resources/nancyfx/parameters.mustache b/modules/swagger-codegen/src/main/resources/nancyfx/parameters.mustache
index e55a82416ec..75486f59f46 100644
--- a/modules/swagger-codegen/src/main/resources/nancyfx/parameters.mustache
+++ b/modules/swagger-codegen/src/main/resources/nancyfx/parameters.mustache
@@ -166,19 +166,19 @@ namespace {{packageName}}.{{packageContext}}.Utils
             parsers.Put(typeof(LocalTime), SafeParse(ParseLocalTime));
             parsers.Put(typeof(LocalTime?), SafeParse(ParseLocalTime));
 
-            parsers.Put(typeof(IEnumerable<string>), value => value);
-            parsers.Put(typeof(ICollection<string>), value => value);
-            parsers.Put(typeof(IList<string>), value => value);
-            parsers.Put(typeof(List<string>), value => value);
-            parsers.Put(typeof(ISet<string>), value => value);
-            parsers.Put(typeof(HashSet<string>), value => value);
-
-            parsers.Put(typeof(IEnumerable<bool>), ImmutableListParse(bool.Parse));
-            parsers.Put(typeof(ICollection<bool>), ImmutableListParse(bool.Parse));
-            parsers.Put(typeof(IList<bool>), ImmutableListParse(bool.Parse));
-            parsers.Put(typeof(List<bool>), ListParse(bool.Parse));
-            parsers.Put(typeof(ISet<bool>), ImmutableSetParse(bool.Parse));
-            parsers.Put(typeof(HashSet<bool>), SetParse(bool.Parse));
+            parsers.Put(typeof(IEnumerable<string>), ImmutableListParse(value => value));
+            parsers.Put(typeof(ICollection<string>), ImmutableListParse(value => value));
+            parsers.Put(typeof(IList<string>), ImmutableListParse(value => value));
+            parsers.Put(typeof(List<string>), ListParse(value => value));
+            parsers.Put(typeof(ISet<string>), ImmutableListParse(value => value));
+            parsers.Put(typeof(HashSet<string>), SetParse(value => value));
+
+            parsers.Put(typeof(IEnumerable<bool?>), NullableImmutableListParse(bool.Parse));
+            parsers.Put(typeof(ICollection<bool?>), NullableImmutableListParse(bool.Parse));
+            parsers.Put(typeof(IList<bool?>), NullableImmutableListParse(bool.Parse));
+            parsers.Put(typeof(List<bool?>), NullableListParse(bool.Parse));
+            parsers.Put(typeof(ISet<bool?>), NullableImmutableSetParse(bool.Parse));
+            parsers.Put(typeof(HashSet<bool?>), NullableSetParse(bool.Parse));
 
             parsers.Put(typeof(IEnumerable<byte>), ImmutableListParse(byte.Parse));
             parsers.Put(typeof(ICollection<byte>), ImmutableListParse(byte.Parse));
@@ -186,6 +186,7 @@ namespace {{packageName}}.{{packageContext}}.Utils
             parsers.Put(typeof(List<byte>), ListParse(byte.Parse));
             parsers.Put(typeof(ISet<byte>), ImmutableSetParse(byte.Parse));
             parsers.Put(typeof(HashSet<byte>), SetParse(byte.Parse));
+
             parsers.Put(typeof(IEnumerable<sbyte>), ImmutableListParse(sbyte.Parse));
             parsers.Put(typeof(ICollection<sbyte>), ImmutableListParse(sbyte.Parse));
             parsers.Put(typeof(IList<sbyte>), ImmutableListParse(sbyte.Parse));
@@ -199,6 +200,7 @@ namespace {{packageName}}.{{packageContext}}.Utils
             parsers.Put(typeof(List<short>), ListParse(short.Parse));
             parsers.Put(typeof(ISet<short>), ImmutableSetParse(short.Parse));
             parsers.Put(typeof(HashSet<short>), SetParse(short.Parse));
+
             parsers.Put(typeof(IEnumerable<ushort>), ImmutableListParse(ushort.Parse));
             parsers.Put(typeof(ICollection<ushort>), ImmutableListParse(ushort.Parse));
             parsers.Put(typeof(IList<ushort>), ImmutableListParse(ushort.Parse));
@@ -206,12 +208,13 @@ namespace {{packageName}}.{{packageContext}}.Utils
             parsers.Put(typeof(ISet<ushort>), ImmutableSetParse(ushort.Parse));
             parsers.Put(typeof(HashSet<ushort>), SetParse(ushort.Parse));
 
-            parsers.Put(typeof(IEnumerable<int>), ImmutableListParse(int.Parse));
-            parsers.Put(typeof(ICollection<int>), ImmutableListParse(int.Parse));
-            parsers.Put(typeof(IList<int>), ImmutableListParse(int.Parse));
-            parsers.Put(typeof(List<int>), ListParse(int.Parse));
-            parsers.Put(typeof(ISet<int>), ImmutableSetParse(int.Parse));
-            parsers.Put(typeof(HashSet<int>), SetParse(int.Parse));
+            parsers.Put(typeof(IEnumerable<int?>), NullableImmutableListParse(int.Parse));
+            parsers.Put(typeof(ICollection<int?>), NullableImmutableListParse(int.Parse));
+            parsers.Put(typeof(IList<int?>), NullableImmutableListParse(int.Parse));
+            parsers.Put(typeof(List<int?>), NullableListParse(int.Parse));
+            parsers.Put(typeof(ISet<int?>), NullableImmutableSetParse(int.Parse));
+            parsers.Put(typeof(HashSet<int?>), NullableSetParse(int.Parse));
+
             parsers.Put(typeof(IEnumerable<uint>), ImmutableListParse(uint.Parse));
             parsers.Put(typeof(ICollection<uint>), ImmutableListParse(uint.Parse));
             parsers.Put(typeof(IList<uint>), ImmutableListParse(uint.Parse));
@@ -219,12 +222,13 @@ namespace {{packageName}}.{{packageContext}}.Utils
             parsers.Put(typeof(ISet<uint>), ImmutableSetParse(uint.Parse));
             parsers.Put(typeof(HashSet<uint>), SetParse(uint.Parse));
 
-            parsers.Put(typeof(IEnumerable<long>), ImmutableListParse(long.Parse));
-            parsers.Put(typeof(ICollection<long>), ImmutableListParse(long.Parse));
-            parsers.Put(typeof(IList<long>), ImmutableListParse(long.Parse));
-            parsers.Put(typeof(List<long>), ListParse(long.Parse));
-            parsers.Put(typeof(ISet<long>), ImmutableSetParse(long.Parse));
-            parsers.Put(typeof(HashSet<long>), SetParse(long.Parse));
+            parsers.Put(typeof(IEnumerable<long?>), NullableImmutableListParse(long.Parse));
+            parsers.Put(typeof(ICollection<long?>), NullableImmutableListParse(long.Parse));
+            parsers.Put(typeof(IList<long?>), NullableImmutableListParse(long.Parse));
+            parsers.Put(typeof(List<long?>), NullableListParse(long.Parse));
+            parsers.Put(typeof(ISet<long?>), NullableImmutableSetParse(long.Parse));
+            parsers.Put(typeof(HashSet<long?>), NullableSetParse(long.Parse));
+
             parsers.Put(typeof(IEnumerable<ulong>), ImmutableListParse(ulong.Parse));
             parsers.Put(typeof(ICollection<ulong>), ImmutableListParse(ulong.Parse));
             parsers.Put(typeof(IList<ulong>), ImmutableListParse(ulong.Parse));
@@ -232,34 +236,33 @@ namespace {{packageName}}.{{packageContext}}.Utils
             parsers.Put(typeof(ISet<ulong>), ImmutableSetParse(ulong.Parse));
             parsers.Put(typeof(HashSet<ulong>), SetParse(ulong.Parse));
 
-            parsers.Put(typeof(IEnumerable<float>), ImmutableListParse(float.Parse));
-            parsers.Put(typeof(ICollection<float>), ImmutableListParse(float.Parse));
-            parsers.Put(typeof(IList<float>), ImmutableListParse(float.Parse));
-            parsers.Put(typeof(List<float>), ListParse(float.Parse));
-            parsers.Put(typeof(ISet<float>), ImmutableSetParse(float.Parse));
-            parsers.Put(typeof(HashSet<float>), SetParse(float.Parse));
-
-            parsers.Put(typeof(IEnumerable<double>), ImmutableListParse(double.Parse));
-            parsers.Put(typeof(ICollection<double>), ImmutableListParse(double.Parse));
-            parsers.Put(typeof(IList<double>), ImmutableListParse(double.Parse));
-            parsers.Put(typeof(List<double>), ListParse(double.Parse));
-            parsers.Put(typeof(ISet<double>), ImmutableSetParse(double.Parse));
-            parsers.Put(typeof(HashSet<double>), SetParse(double.Parse));
-
-            parsers.Put(typeof(IEnumerable<decimal>), ImmutableListParse(decimal.Parse));
-            parsers.Put(typeof(ICollection<decimal>), ImmutableListParse(decimal.Parse));
-            parsers.Put(typeof(IList<decimal>), ImmutableListParse(decimal.Parse));
-            parsers.Put(typeof(List<decimal>), ListParse(decimal.Parse));
-            parsers.Put(typeof(ISet<decimal>), ImmutableSetParse(decimal.Parse));
-            parsers.Put(typeof(HashSet<decimal>), SetParse(decimal.Parse));
-
-
-            parsers.Put(typeof(IEnumerable<DateTime>), ImmutableListParse(DateTime.Parse));
-            parsers.Put(typeof(ICollection<DateTime>), ImmutableListParse(DateTime.Parse));
-            parsers.Put(typeof(IList<DateTime>), ImmutableListParse(DateTime.Parse));
-            parsers.Put(typeof(List<DateTime>), ListParse(DateTime.Parse));
-            parsers.Put(typeof(ISet<DateTime>), ImmutableSetParse(DateTime.Parse));
-            parsers.Put(typeof(HashSet<DateTime>), SetParse(DateTime.Parse));
+            parsers.Put(typeof(IEnumerable<float?>), NullableImmutableListParse(float.Parse));
+            parsers.Put(typeof(ICollection<float?>), NullableImmutableListParse(float.Parse));
+            parsers.Put(typeof(IList<float?>), NullableImmutableListParse(float.Parse));
+            parsers.Put(typeof(List<float?>), NullableListParse(float.Parse));
+            parsers.Put(typeof(ISet<float?>), NullableImmutableSetParse(float.Parse));
+            parsers.Put(typeof(HashSet<float?>), NullableSetParse(float.Parse));
+
+            parsers.Put(typeof(IEnumerable<double?>), NullableImmutableListParse(double.Parse));
+            parsers.Put(typeof(ICollection<double?>), NullableImmutableListParse(double.Parse));
+            parsers.Put(typeof(IList<double?>), NullableImmutableListParse(double.Parse));
+            parsers.Put(typeof(List<double?>), NullableListParse(double.Parse));
+            parsers.Put(typeof(ISet<double?>), NullableImmutableSetParse(double.Parse));
+            parsers.Put(typeof(HashSet<double?>), NullableSetParse(double.Parse));
+
+            parsers.Put(typeof(IEnumerable<decimal?>), NullableImmutableListParse(decimal.Parse));
+            parsers.Put(typeof(ICollection<decimal?>), NullableImmutableListParse(decimal.Parse));
+            parsers.Put(typeof(IList<decimal?>), NullableImmutableListParse(decimal.Parse));
+            parsers.Put(typeof(List<decimal?>), NullableListParse(decimal.Parse));
+            parsers.Put(typeof(ISet<decimal?>), NullableImmutableSetParse(decimal.Parse));
+            parsers.Put(typeof(HashSet<decimal?>), NullableSetParse(decimal.Parse));
+
+            parsers.Put(typeof(IEnumerable<DateTime?>), NullableImmutableListParse(DateTime.Parse));
+            parsers.Put(typeof(ICollection<DateTime?>), NullableImmutableListParse(DateTime.Parse));
+            parsers.Put(typeof(IList<DateTime?>), NullableImmutableListParse(DateTime.Parse));
+            parsers.Put(typeof(List<DateTime?>), NullableListParse(DateTime.Parse));
+            parsers.Put(typeof(ISet<DateTime?>), NullableImmutableSetParse(DateTime.Parse));
+            parsers.Put(typeof(HashSet<DateTime?>), NullableSetParse(DateTime.Parse));
 
             parsers.Put(typeof(IEnumerable<TimeSpan>), ImmutableListParse(TimeSpan.Parse));
             parsers.Put(typeof(ICollection<TimeSpan>), ImmutableListParse(TimeSpan.Parse));
@@ -295,6 +298,11 @@ namespace {{packageName}}.{{packageContext}}.Utils
             };
         }
 
+        private static Func<Parameter, object> NullableListParse<T>(Func<string, T> itemParser) where T: struct
+        {
+            return ListParse(it => it.ToNullable(itemParser));
+        }
+
         private static Func<Parameter, object> ListParse<T>(Func<string, T> itemParser)
         {
             return parameter =>
@@ -303,15 +311,15 @@ namespace {{packageName}}.{{packageContext}}.Utils
                 {
                     return new List<T>();
                 }
-                var results = parameter.Value.Split(new[] { ',' }, StringSplitOptions.None)
-                    .Where(it => it != null)
-                    .Select(it => it.Trim())
-                    .Select(itemParser)
-                    .ToList();
-                return results;
+                return ParseCollection(parameter.Value, itemParser).ToList();
             };
         }
 
+        private static Func<Parameter, object> NullableImmutableListParse<T>(Func<string, T> itemParser) where T: struct
+        {
+            return ImmutableListParse(it => it.ToNullable(itemParser));
+        }
+
         private static Func<Parameter, object> ImmutableListParse<T>(Func<string, T> itemParser)
         {
             return parameter =>
@@ -320,15 +328,15 @@ namespace {{packageName}}.{{packageContext}}.Utils
                 {
                     return Lists.EmptyList<T>();
                 }
-                var results = parameter.Value.Split(new[] { ',' }, StringSplitOptions.None)
-                    .Where(it => it != null)
-                    .Select(it => it.Trim())
-                    .Select(itemParser)
-                    .ToImmutableList();
-                return results;
+                return ParseCollection(parameter.Value, itemParser).ToImmutableList();
             };
         }
 
+        private static Func<Parameter, object> NullableSetParse<T>(Func<string, T> itemParser) where T: struct
+        {
+            return SetParse(it => it.ToNullable(itemParser));
+        }
+
         private static Func<Parameter, object> SetParse<T>(Func<string, T> itemParser)
         {
             return parameter =>
@@ -337,15 +345,15 @@ namespace {{packageName}}.{{packageContext}}.Utils
                 {
                     return new HashSet<T>();
                 }
-                var results = parameter.Value.Split(new[] { ',' }, StringSplitOptions.None)
-                    .Where(it => it != null)
-                    .Select(it => it.Trim())
-                    .Select(itemParser)
-                    .ToSet();
-                return results;
+                return ParseCollection(parameter.Value, itemParser).ToSet();
             };
         }
 
+        private static Func<Parameter, object> NullableImmutableSetParse<T>(Func<string, T> itemParser) where T: struct
+        {
+            return ImmutableSetParse(it => it.ToNullable(itemParser));
+        }
+
         private static Func<Parameter, object> ImmutableSetParse<T>(Func<string, T> itemParser)
         {
             return parameter =>
@@ -354,12 +362,7 @@ namespace {{packageName}}.{{packageContext}}.Utils
                 {
                     return Sets.EmptySet<T>();
                 }
-                var results = parameter.Value.Split(new[] { ',' }, StringSplitOptions.None)
-                    .Where(it => it != null)
-                    .Select(it => it.Trim())
-                    .Select(itemParser)
-                    .ToImmutableHashSet();
-                return results;
+                return ParseCollection(parameter.Value, itemParser).ToImmutableHashSet();
             };
         }
 
@@ -386,6 +389,32 @@ namespace {{packageName}}.{{packageContext}}.Utils
                 parameter.Name, parameter.Value, type));
         }
 
+        private static IEnumerable<T> ParseCollection<T>(string value, Func<string, T> itemParser)
+        {
+            var results = value.Split(new[] { ',' }, StringSplitOptions.None)
+                        .Where(it => it != null)
+                        .Select(it => it.Trim())
+                        .Select(itemParser);
+            return results;
+        }
+
+        public static T? ToNullable<T>(this string s, Func<string, T> itemParser) where T : struct
+        {
+            T? result = new T?();
+            try
+            {
+                if (!string.IsNullOrEmpty(s) && s.Trim().Length > 0)
+                {
+                    result = itemParser(s);
+                }
+            }
+            catch (Exception e)
+            {
+                throw new InvalidOperationException(Strings.Format("Unable to parse value: '{0}' to nullable: '{1}'", s, typeof(T).ToString()), e);
+            }
+            return result;
+        }
+
         private class Parameter
         {
             internal string Name { get; private set; }
diff --git a/samples/server/petstore/nancyfx/IO.Swagger.sln b/samples/server/petstore/nancyfx/IO.Swagger.sln
index e6fd22af6f6..09301395de7 100644
--- a/samples/server/petstore/nancyfx/IO.Swagger.sln
+++ b/samples/server/petstore/nancyfx/IO.Swagger.sln
@@ -2,7 +2,7 @@ Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 2012
 VisualStudioVersion = 12.0.0.0
 MinimumVisualStudioVersion = 10.0.0.1
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "IO.Swagger", "src\IO.Swagger\IO.Swagger.csproj", "{7D50D142-14E1-4E99-842B-18D3AF159948}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "IO.Swagger", "src\IO.Swagger\IO.Swagger.csproj", "{3B55ED13-A471-44B1-A8D5-C158723C0A0C}"
 EndProject
 Global
 GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -10,17 +10,10 @@ Debug|Any CPU = Debug|Any CPU
 Release|Any CPU = Release|Any CPU
 EndGlobalSection
 GlobalSection(ProjectConfigurationPlatforms) = postSolution
-<<<<<<< HEAD
-{7D50D142-14E1-4E99-842B-18D3AF159948}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-{7D50D142-14E1-4E99-842B-18D3AF159948}.Debug|Any CPU.Build.0 = Debug|Any CPU
-{7D50D142-14E1-4E99-842B-18D3AF159948}.Release|Any CPU.ActiveCfg = Release|Any CPU
-{7D50D142-14E1-4E99-842B-18D3AF159948}.Release|Any CPU.Build.0 = Release|Any CPU
-=======
-{1CE943E7-586D-4D9C-BE8B-3E005FDC39D1}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-{1CE943E7-586D-4D9C-BE8B-3E005FDC39D1}.Debug|Any CPU.Build.0 = Debug|Any CPU
-{1CE943E7-586D-4D9C-BE8B-3E005FDC39D1}.Release|Any CPU.ActiveCfg = Release|Any CPU
-{1CE943E7-586D-4D9C-BE8B-3E005FDC39D1}.Release|Any CPU.Build.0 = Release|Any CPU
->>>>>>> 92c474b2c235f4635e4be43a97c7941fec64dc82
+{3B55ED13-A471-44B1-A8D5-C158723C0A0C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+{3B55ED13-A471-44B1-A8D5-C158723C0A0C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+{3B55ED13-A471-44B1-A8D5-C158723C0A0C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+{3B55ED13-A471-44B1-A8D5-C158723C0A0C}.Release|Any CPU.Build.0 = Release|Any CPU
 {19F1DEBC-DE5E-4517-8062-F000CD499087}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 {19F1DEBC-DE5E-4517-8062-F000CD499087}.Debug|Any CPU.Build.0 = Debug|Any CPU
 {19F1DEBC-DE5E-4517-8062-F000CD499087}.Release|Any CPU.ActiveCfg = Release|Any CPU
@@ -29,4 +22,4 @@ EndGlobalSection
 GlobalSection(SolutionProperties) = preSolution
 HideSolutionNode = FALSE
 EndGlobalSection
-EndGlobal
+EndGlobal
\ No newline at end of file
diff --git a/samples/server/petstore/nancyfx/src/IO.Swagger/IO.Swagger.csproj b/samples/server/petstore/nancyfx/src/IO.Swagger/IO.Swagger.csproj
index 60535f7aae6..a103786b912 100644
--- a/samples/server/petstore/nancyfx/src/IO.Swagger/IO.Swagger.csproj
+++ b/samples/server/petstore/nancyfx/src/IO.Swagger/IO.Swagger.csproj
@@ -3,7 +3,7 @@
     <PropertyGroup>
         <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
         <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
-        <ProjectGuid>{7D50D142-14E1-4E99-842B-18D3AF159948}</ProjectGuid>
+        <ProjectGuid>{3B55ED13-A471-44B1-A8D5-C158723C0A0C}</ProjectGuid>
         <OutputType>Library</OutputType>
         <AppDesignerFolder>Properties</AppDesignerFolder>
         <RootNamespace>IO.Swagger.v2</RootNamespace>
@@ -63,3 +63,4 @@
     </ItemGroup>
     <Import Project="$(MsBuildToolsPath)\Microsoft.CSharp.targets"/>
 </Project>
+
diff --git a/samples/server/petstore/nancyfx/src/IO.Swagger/Modules/PetModule.cs b/samples/server/petstore/nancyfx/src/IO.Swagger/Modules/PetModule.cs
index d6922531e24..edfa0ecac4a 100644
--- a/samples/server/petstore/nancyfx/src/IO.Swagger/Modules/PetModule.cs
+++ b/samples/server/petstore/nancyfx/src/IO.Swagger/Modules/PetModule.cs
@@ -55,7 +55,7 @@ public PetModule(PetService service) : base("/v2")
                 var status = Parameters.ValueOf<FindPetsByStatusStatusEnum?>(parameters, Context.Request, "status", ParameterType.Query);
                 Preconditions.IsNotNull(status, "Required parameter: 'status' is missing at 'FindPetsByStatus'");
                 
-                return service.FindPetsByStatus(Context, status);
+                return service.FindPetsByStatus(Context, status).ToArray();
             };
 
             Get["/pet/findByTags"] = parameters =>
@@ -63,7 +63,7 @@ public PetModule(PetService service) : base("/v2")
                 var tags = Parameters.ValueOf<List<string>>(parameters, Context.Request, "tags", ParameterType.Query);
                 Preconditions.IsNotNull(tags, "Required parameter: 'tags' is missing at 'FindPetsByTags'");
                 
-                return service.FindPetsByTags(Context, tags);
+                return service.FindPetsByTags(Context, tags).ToArray();
             };
 
             Get["/pet/{petId}"] = parameters =>
diff --git a/samples/server/petstore/nancyfx/src/IO.Swagger/Utils/Parameters.cs b/samples/server/petstore/nancyfx/src/IO.Swagger/Utils/Parameters.cs
index 7f0e848f98a..6175758fd9a 100644
--- a/samples/server/petstore/nancyfx/src/IO.Swagger/Utils/Parameters.cs
+++ b/samples/server/petstore/nancyfx/src/IO.Swagger/Utils/Parameters.cs
@@ -166,19 +166,19 @@ private static IDictionary<Type, Func<Parameter, object>> CreateParsers()
             parsers.Put(typeof(LocalTime), SafeParse(ParseLocalTime));
             parsers.Put(typeof(LocalTime?), SafeParse(ParseLocalTime));
 
-            parsers.Put(typeof(IEnumerable<string>), value => value);
-            parsers.Put(typeof(ICollection<string>), value => value);
-            parsers.Put(typeof(IList<string>), value => value);
-            parsers.Put(typeof(List<string>), value => value);
-            parsers.Put(typeof(ISet<string>), value => value);
-            parsers.Put(typeof(HashSet<string>), value => value);
-
-            parsers.Put(typeof(IEnumerable<bool>), ImmutableListParse(bool.Parse));
-            parsers.Put(typeof(ICollection<bool>), ImmutableListParse(bool.Parse));
-            parsers.Put(typeof(IList<bool>), ImmutableListParse(bool.Parse));
-            parsers.Put(typeof(List<bool>), ListParse(bool.Parse));
-            parsers.Put(typeof(ISet<bool>), ImmutableSetParse(bool.Parse));
-            parsers.Put(typeof(HashSet<bool>), SetParse(bool.Parse));
+            parsers.Put(typeof(IEnumerable<string>), ImmutableListParse(value => value));
+            parsers.Put(typeof(ICollection<string>), ImmutableListParse(value => value));
+            parsers.Put(typeof(IList<string>), ImmutableListParse(value => value));
+            parsers.Put(typeof(List<string>), ListParse(value => value));
+            parsers.Put(typeof(ISet<string>), ImmutableListParse(value => value));
+            parsers.Put(typeof(HashSet<string>), SetParse(value => value));
+
+            parsers.Put(typeof(IEnumerable<bool?>), NullableImmutableListParse(bool.Parse));
+            parsers.Put(typeof(ICollection<bool?>), NullableImmutableListParse(bool.Parse));
+            parsers.Put(typeof(IList<bool?>), NullableImmutableListParse(bool.Parse));
+            parsers.Put(typeof(List<bool?>), NullableListParse(bool.Parse));
+            parsers.Put(typeof(ISet<bool?>), NullableImmutableSetParse(bool.Parse));
+            parsers.Put(typeof(HashSet<bool?>), NullableSetParse(bool.Parse));
 
             parsers.Put(typeof(IEnumerable<byte>), ImmutableListParse(byte.Parse));
             parsers.Put(typeof(ICollection<byte>), ImmutableListParse(byte.Parse));
@@ -186,6 +186,7 @@ private static IDictionary<Type, Func<Parameter, object>> CreateParsers()
             parsers.Put(typeof(List<byte>), ListParse(byte.Parse));
             parsers.Put(typeof(ISet<byte>), ImmutableSetParse(byte.Parse));
             parsers.Put(typeof(HashSet<byte>), SetParse(byte.Parse));
+
             parsers.Put(typeof(IEnumerable<sbyte>), ImmutableListParse(sbyte.Parse));
             parsers.Put(typeof(ICollection<sbyte>), ImmutableListParse(sbyte.Parse));
             parsers.Put(typeof(IList<sbyte>), ImmutableListParse(sbyte.Parse));
@@ -199,6 +200,7 @@ private static IDictionary<Type, Func<Parameter, object>> CreateParsers()
             parsers.Put(typeof(List<short>), ListParse(short.Parse));
             parsers.Put(typeof(ISet<short>), ImmutableSetParse(short.Parse));
             parsers.Put(typeof(HashSet<short>), SetParse(short.Parse));
+
             parsers.Put(typeof(IEnumerable<ushort>), ImmutableListParse(ushort.Parse));
             parsers.Put(typeof(ICollection<ushort>), ImmutableListParse(ushort.Parse));
             parsers.Put(typeof(IList<ushort>), ImmutableListParse(ushort.Parse));
@@ -206,12 +208,13 @@ private static IDictionary<Type, Func<Parameter, object>> CreateParsers()
             parsers.Put(typeof(ISet<ushort>), ImmutableSetParse(ushort.Parse));
             parsers.Put(typeof(HashSet<ushort>), SetParse(ushort.Parse));
 
-            parsers.Put(typeof(IEnumerable<int>), ImmutableListParse(int.Parse));
-            parsers.Put(typeof(ICollection<int>), ImmutableListParse(int.Parse));
-            parsers.Put(typeof(IList<int>), ImmutableListParse(int.Parse));
-            parsers.Put(typeof(List<int>), ListParse(int.Parse));
-            parsers.Put(typeof(ISet<int>), ImmutableSetParse(int.Parse));
-            parsers.Put(typeof(HashSet<int>), SetParse(int.Parse));
+            parsers.Put(typeof(IEnumerable<int?>), NullableImmutableListParse(int.Parse));
+            parsers.Put(typeof(ICollection<int?>), NullableImmutableListParse(int.Parse));
+            parsers.Put(typeof(IList<int?>), NullableImmutableListParse(int.Parse));
+            parsers.Put(typeof(List<int?>), NullableListParse(int.Parse));
+            parsers.Put(typeof(ISet<int?>), NullableImmutableSetParse(int.Parse));
+            parsers.Put(typeof(HashSet<int?>), NullableSetParse(int.Parse));
+
             parsers.Put(typeof(IEnumerable<uint>), ImmutableListParse(uint.Parse));
             parsers.Put(typeof(ICollection<uint>), ImmutableListParse(uint.Parse));
             parsers.Put(typeof(IList<uint>), ImmutableListParse(uint.Parse));
@@ -219,12 +222,13 @@ private static IDictionary<Type, Func<Parameter, object>> CreateParsers()
             parsers.Put(typeof(ISet<uint>), ImmutableSetParse(uint.Parse));
             parsers.Put(typeof(HashSet<uint>), SetParse(uint.Parse));
 
-            parsers.Put(typeof(IEnumerable<long>), ImmutableListParse(long.Parse));
-            parsers.Put(typeof(ICollection<long>), ImmutableListParse(long.Parse));
-            parsers.Put(typeof(IList<long>), ImmutableListParse(long.Parse));
-            parsers.Put(typeof(List<long>), ListParse(long.Parse));
-            parsers.Put(typeof(ISet<long>), ImmutableSetParse(long.Parse));
-            parsers.Put(typeof(HashSet<long>), SetParse(long.Parse));
+            parsers.Put(typeof(IEnumerable<long?>), NullableImmutableListParse(long.Parse));
+            parsers.Put(typeof(ICollection<long?>), NullableImmutableListParse(long.Parse));
+            parsers.Put(typeof(IList<long?>), NullableImmutableListParse(long.Parse));
+            parsers.Put(typeof(List<long?>), NullableListParse(long.Parse));
+            parsers.Put(typeof(ISet<long?>), NullableImmutableSetParse(long.Parse));
+            parsers.Put(typeof(HashSet<long?>), NullableSetParse(long.Parse));
+
             parsers.Put(typeof(IEnumerable<ulong>), ImmutableListParse(ulong.Parse));
             parsers.Put(typeof(ICollection<ulong>), ImmutableListParse(ulong.Parse));
             parsers.Put(typeof(IList<ulong>), ImmutableListParse(ulong.Parse));
@@ -232,34 +236,33 @@ private static IDictionary<Type, Func<Parameter, object>> CreateParsers()
             parsers.Put(typeof(ISet<ulong>), ImmutableSetParse(ulong.Parse));
             parsers.Put(typeof(HashSet<ulong>), SetParse(ulong.Parse));
 
-            parsers.Put(typeof(IEnumerable<float>), ImmutableListParse(float.Parse));
-            parsers.Put(typeof(ICollection<float>), ImmutableListParse(float.Parse));
-            parsers.Put(typeof(IList<float>), ImmutableListParse(float.Parse));
-            parsers.Put(typeof(List<float>), ListParse(float.Parse));
-            parsers.Put(typeof(ISet<float>), ImmutableSetParse(float.Parse));
-            parsers.Put(typeof(HashSet<float>), SetParse(float.Parse));
-
-            parsers.Put(typeof(IEnumerable<double>), ImmutableListParse(double.Parse));
-            parsers.Put(typeof(ICollection<double>), ImmutableListParse(double.Parse));
-            parsers.Put(typeof(IList<double>), ImmutableListParse(double.Parse));
-            parsers.Put(typeof(List<double>), ListParse(double.Parse));
-            parsers.Put(typeof(ISet<double>), ImmutableSetParse(double.Parse));
-            parsers.Put(typeof(HashSet<double>), SetParse(double.Parse));
-
-            parsers.Put(typeof(IEnumerable<decimal>), ImmutableListParse(decimal.Parse));
-            parsers.Put(typeof(ICollection<decimal>), ImmutableListParse(decimal.Parse));
-            parsers.Put(typeof(IList<decimal>), ImmutableListParse(decimal.Parse));
-            parsers.Put(typeof(List<decimal>), ListParse(decimal.Parse));
-            parsers.Put(typeof(ISet<decimal>), ImmutableSetParse(decimal.Parse));
-            parsers.Put(typeof(HashSet<decimal>), SetParse(decimal.Parse));
-
-
-            parsers.Put(typeof(IEnumerable<DateTime>), ImmutableListParse(DateTime.Parse));
-            parsers.Put(typeof(ICollection<DateTime>), ImmutableListParse(DateTime.Parse));
-            parsers.Put(typeof(IList<DateTime>), ImmutableListParse(DateTime.Parse));
-            parsers.Put(typeof(List<DateTime>), ListParse(DateTime.Parse));
-            parsers.Put(typeof(ISet<DateTime>), ImmutableSetParse(DateTime.Parse));
-            parsers.Put(typeof(HashSet<DateTime>), SetParse(DateTime.Parse));
+            parsers.Put(typeof(IEnumerable<float?>), NullableImmutableListParse(float.Parse));
+            parsers.Put(typeof(ICollection<float?>), NullableImmutableListParse(float.Parse));
+            parsers.Put(typeof(IList<float?>), NullableImmutableListParse(float.Parse));
+            parsers.Put(typeof(List<float?>), NullableListParse(float.Parse));
+            parsers.Put(typeof(ISet<float?>), NullableImmutableSetParse(float.Parse));
+            parsers.Put(typeof(HashSet<float?>), NullableSetParse(float.Parse));
+
+            parsers.Put(typeof(IEnumerable<double?>), NullableImmutableListParse(double.Parse));
+            parsers.Put(typeof(ICollection<double?>), NullableImmutableListParse(double.Parse));
+            parsers.Put(typeof(IList<double?>), NullableImmutableListParse(double.Parse));
+            parsers.Put(typeof(List<double?>), NullableListParse(double.Parse));
+            parsers.Put(typeof(ISet<double?>), NullableImmutableSetParse(double.Parse));
+            parsers.Put(typeof(HashSet<double?>), NullableSetParse(double.Parse));
+
+            parsers.Put(typeof(IEnumerable<decimal?>), NullableImmutableListParse(decimal.Parse));
+            parsers.Put(typeof(ICollection<decimal?>), NullableImmutableListParse(decimal.Parse));
+            parsers.Put(typeof(IList<decimal?>), NullableImmutableListParse(decimal.Parse));
+            parsers.Put(typeof(List<decimal?>), NullableListParse(decimal.Parse));
+            parsers.Put(typeof(ISet<decimal?>), NullableImmutableSetParse(decimal.Parse));
+            parsers.Put(typeof(HashSet<decimal?>), NullableSetParse(decimal.Parse));
+
+            parsers.Put(typeof(IEnumerable<DateTime?>), NullableImmutableListParse(DateTime.Parse));
+            parsers.Put(typeof(ICollection<DateTime?>), NullableImmutableListParse(DateTime.Parse));
+            parsers.Put(typeof(IList<DateTime?>), NullableImmutableListParse(DateTime.Parse));
+            parsers.Put(typeof(List<DateTime?>), NullableListParse(DateTime.Parse));
+            parsers.Put(typeof(ISet<DateTime?>), NullableImmutableSetParse(DateTime.Parse));
+            parsers.Put(typeof(HashSet<DateTime?>), NullableSetParse(DateTime.Parse));
 
             parsers.Put(typeof(IEnumerable<TimeSpan>), ImmutableListParse(TimeSpan.Parse));
             parsers.Put(typeof(ICollection<TimeSpan>), ImmutableListParse(TimeSpan.Parse));
@@ -295,6 +298,11 @@ private static Func<Parameter, object> SafeParse<T>(Func<string, T> parse)
             };
         }
 
+        private static Func<Parameter, object> NullableListParse<T>(Func<string, T> itemParser) where T: struct
+        {
+            return ListParse(it => it.ToNullable(itemParser));
+        }
+
         private static Func<Parameter, object> ListParse<T>(Func<string, T> itemParser)
         {
             return parameter =>
@@ -303,15 +311,15 @@ private static Func<Parameter, object> ListParse<T>(Func<string, T> itemParser)
                 {
                     return new List<T>();
                 }
-                var results = parameter.Value.Split(new[] { ',' }, StringSplitOptions.None)
-                    .Where(it => it != null)
-                    .Select(it => it.Trim())
-                    .Select(itemParser)
-                    .ToList();
-                return results;
+                return ParseCollection(parameter.Value, itemParser).ToList();
             };
         }
 
+        private static Func<Parameter, object> NullableImmutableListParse<T>(Func<string, T> itemParser) where T: struct
+        {
+            return ImmutableListParse(it => it.ToNullable(itemParser));
+        }
+
         private static Func<Parameter, object> ImmutableListParse<T>(Func<string, T> itemParser)
         {
             return parameter =>
@@ -320,15 +328,15 @@ private static Func<Parameter, object> ImmutableListParse<T>(Func<string, T> ite
                 {
                     return Lists.EmptyList<T>();
                 }
-                var results = parameter.Value.Split(new[] { ',' }, StringSplitOptions.None)
-                    .Where(it => it != null)
-                    .Select(it => it.Trim())
-                    .Select(itemParser)
-                    .ToImmutableList();
-                return results;
+                return ParseCollection(parameter.Value, itemParser).ToImmutableList();
             };
         }
 
+        private static Func<Parameter, object> NullableSetParse<T>(Func<string, T> itemParser) where T: struct
+        {
+            return SetParse(it => it.ToNullable(itemParser));
+        }
+
         private static Func<Parameter, object> SetParse<T>(Func<string, T> itemParser)
         {
             return parameter =>
@@ -337,15 +345,15 @@ private static Func<Parameter, object> SetParse<T>(Func<string, T> itemParser)
                 {
                     return new HashSet<T>();
                 }
-                var results = parameter.Value.Split(new[] { ',' }, StringSplitOptions.None)
-                    .Where(it => it != null)
-                    .Select(it => it.Trim())
-                    .Select(itemParser)
-                    .ToSet();
-                return results;
+                return ParseCollection(parameter.Value, itemParser).ToSet();
             };
         }
 
+        private static Func<Parameter, object> NullableImmutableSetParse<T>(Func<string, T> itemParser) where T: struct
+        {
+            return ImmutableSetParse(it => it.ToNullable(itemParser));
+        }
+
         private static Func<Parameter, object> ImmutableSetParse<T>(Func<string, T> itemParser)
         {
             return parameter =>
@@ -354,12 +362,7 @@ private static Func<Parameter, object> ImmutableSetParse<T>(Func<string, T> item
                 {
                     return Sets.EmptySet<T>();
                 }
-                var results = parameter.Value.Split(new[] { ',' }, StringSplitOptions.None)
-                    .Where(it => it != null)
-                    .Select(it => it.Trim())
-                    .Select(itemParser)
-                    .ToImmutableHashSet();
-                return results;
+                return ParseCollection(parameter.Value, itemParser).ToImmutableHashSet();
             };
         }
 
@@ -386,6 +389,32 @@ private static ArgumentException InvalidParameterFormat(Parameter parameter, Typ
                 parameter.Name, parameter.Value, type));
         }
 
+        private static IEnumerable<T> ParseCollection<T>(string value, Func<string, T> itemParser)
+        {
+            var results = value.Split(new[] { ',' }, StringSplitOptions.None)
+                        .Where(it => it != null)
+                        .Select(it => it.Trim())
+                        .Select(itemParser);
+            return results;
+        }
+
+        public static T? ToNullable<T>(this string s, Func<string, T> itemParser) where T : struct
+        {
+            T? result = new T?();
+            try
+            {
+                if (!string.IsNullOrEmpty(s) && s.Trim().Length > 0)
+                {
+                    result = itemParser(s);
+                }
+            }
+            catch (Exception e)
+            {
+                throw new InvalidOperationException(Strings.Format("Unable to parse value: '{0}' to nullable: '{1}'", s, typeof(T).ToString()), e);
+            }
+            return result;
+        }
+
         private class Parameter
         {
             internal string Name { get; private set; }