diff --git a/modules/openapi-generator/src/main/resources/csharp/auth/TokenResponse.mustache b/modules/openapi-generator/src/main/resources/csharp/auth/TokenResponse.mustache
index 443479677a9..becd82d87a1 100644
--- a/modules/openapi-generator/src/main/resources/csharp/auth/TokenResponse.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp/auth/TokenResponse.mustache
@@ -1,5 +1,6 @@
 {{>partial_header}}
 
+using System;
 using Newtonsoft.Json;
 
 namespace {{packageName}}.Client.Auth
@@ -13,7 +14,7 @@ namespace {{packageName}}.Client.Auth
         [JsonProperty("expires_in")]
         public int? ExpiresIn { get; set; }
         [JsonProperty("created")]
-        public DateTime Created { get; set; }
+        public DateTime? Created { get; set; }
 
         [JsonProperty("refresh_token")]
         public string{{nrt?}} RefreshToken { get; set; }
diff --git a/samples/client/petstore/csharp/restsharp/net4.7/MultipleFrameworks/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs b/samples/client/petstore/csharp/restsharp/net4.7/MultipleFrameworks/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
index a207ffbfe1c..ab1cf58090d 100644
--- a/samples/client/petstore/csharp/restsharp/net4.7/MultipleFrameworks/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
+++ b/samples/client/petstore/csharp/restsharp/net4.7/MultipleFrameworks/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
@@ -8,6 +8,7 @@
  */
 
 
+using System;
 using Newtonsoft.Json;
 
 namespace Org.OpenAPITools.Client.Auth
@@ -21,7 +22,7 @@ namespace Org.OpenAPITools.Client.Auth
         [JsonProperty("expires_in")]
         public int? ExpiresIn { get; set; }
         [JsonProperty("created")]
-        public DateTime Created { get; set; }
+        public DateTime? Created { get; set; }
 
         [JsonProperty("refresh_token")]
         public string RefreshToken { get; set; }
diff --git a/samples/client/petstore/csharp/restsharp/net4.7/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs b/samples/client/petstore/csharp/restsharp/net4.7/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
index e91974b99a2..d3703f73dd7 100644
--- a/samples/client/petstore/csharp/restsharp/net4.7/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
+++ b/samples/client/petstore/csharp/restsharp/net4.7/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
@@ -8,6 +8,7 @@
  */
 
 
+using System;
 using Newtonsoft.Json;
 
 namespace Org.OpenAPITools.Client.Auth
@@ -21,7 +22,7 @@ namespace Org.OpenAPITools.Client.Auth
         [JsonProperty("expires_in")]
         public int? ExpiresIn { get; set; }
         [JsonProperty("created")]
-        public DateTime Created { get; set; }
+        public DateTime? Created { get; set; }
 
         [JsonProperty("refresh_token")]
         public string RefreshToken { get; set; }
diff --git a/samples/client/petstore/csharp/restsharp/net4.8/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs b/samples/client/petstore/csharp/restsharp/net4.8/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
index e91974b99a2..d3703f73dd7 100644
--- a/samples/client/petstore/csharp/restsharp/net4.8/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
+++ b/samples/client/petstore/csharp/restsharp/net4.8/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
@@ -8,6 +8,7 @@
  */
 
 
+using System;
 using Newtonsoft.Json;
 
 namespace Org.OpenAPITools.Client.Auth
@@ -21,7 +22,7 @@ namespace Org.OpenAPITools.Client.Auth
         [JsonProperty("expires_in")]
         public int? ExpiresIn { get; set; }
         [JsonProperty("created")]
-        public DateTime Created { get; set; }
+        public DateTime? Created { get; set; }
 
         [JsonProperty("refresh_token")]
         public string RefreshToken { get; set; }
diff --git a/samples/client/petstore/csharp/restsharp/net7/EnumMappings/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs b/samples/client/petstore/csharp/restsharp/net7/EnumMappings/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
index 4f525b9940e..9b9fc94bbf8 100644
--- a/samples/client/petstore/csharp/restsharp/net7/EnumMappings/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
+++ b/samples/client/petstore/csharp/restsharp/net7/EnumMappings/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
@@ -8,6 +8,7 @@
  */
 
 
+using System;
 using Newtonsoft.Json;
 
 namespace Org.OpenAPITools.Client.Auth
@@ -21,7 +22,7 @@ namespace Org.OpenAPITools.Client.Auth
         [JsonProperty("expires_in")]
         public int? ExpiresIn { get; set; }
         [JsonProperty("created")]
-        public DateTime Created { get; set; }
+        public DateTime? Created { get; set; }
 
         [JsonProperty("refresh_token")]
         public string? RefreshToken { get; set; }
diff --git a/samples/client/petstore/csharp/restsharp/net7/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs b/samples/client/petstore/csharp/restsharp/net7/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
index 4f525b9940e..9b9fc94bbf8 100644
--- a/samples/client/petstore/csharp/restsharp/net7/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
+++ b/samples/client/petstore/csharp/restsharp/net7/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
@@ -8,6 +8,7 @@
  */
 
 
+using System;
 using Newtonsoft.Json;
 
 namespace Org.OpenAPITools.Client.Auth
@@ -21,7 +22,7 @@ namespace Org.OpenAPITools.Client.Auth
         [JsonProperty("expires_in")]
         public int? ExpiresIn { get; set; }
         [JsonProperty("created")]
-        public DateTime Created { get; set; }
+        public DateTime? Created { get; set; }
 
         [JsonProperty("refresh_token")]
         public string? RefreshToken { get; set; }
diff --git a/samples/client/petstore/csharp/restsharp/standard2.0/ConditionalSerialization/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs b/samples/client/petstore/csharp/restsharp/standard2.0/ConditionalSerialization/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
index e91974b99a2..d3703f73dd7 100644
--- a/samples/client/petstore/csharp/restsharp/standard2.0/ConditionalSerialization/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
+++ b/samples/client/petstore/csharp/restsharp/standard2.0/ConditionalSerialization/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
@@ -8,6 +8,7 @@
  */
 
 
+using System;
 using Newtonsoft.Json;
 
 namespace Org.OpenAPITools.Client.Auth
@@ -21,7 +22,7 @@ namespace Org.OpenAPITools.Client.Auth
         [JsonProperty("expires_in")]
         public int? ExpiresIn { get; set; }
         [JsonProperty("created")]
-        public DateTime Created { get; set; }
+        public DateTime? Created { get; set; }
 
         [JsonProperty("refresh_token")]
         public string RefreshToken { get; set; }
diff --git a/samples/client/petstore/csharp/restsharp/standard2.0/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs b/samples/client/petstore/csharp/restsharp/standard2.0/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
index e91974b99a2..d3703f73dd7 100644
--- a/samples/client/petstore/csharp/restsharp/standard2.0/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
+++ b/samples/client/petstore/csharp/restsharp/standard2.0/Petstore/src/Org.OpenAPITools/Client/Auth/TokenResponse.cs
@@ -8,6 +8,7 @@
  */
 
 
+using System;
 using Newtonsoft.Json;
 
 namespace Org.OpenAPITools.Client.Auth
@@ -21,7 +22,7 @@ namespace Org.OpenAPITools.Client.Auth
         [JsonProperty("expires_in")]
         public int? ExpiresIn { get; set; }
         [JsonProperty("created")]
-        public DateTime Created { get; set; }
+        public DateTime? Created { get; set; }
 
         [JsonProperty("refresh_token")]
         public string RefreshToken { get; set; }