diff --git a/modules/openapi-generator/src/main/resources/csharp-netcore/ClientUtils.mustache b/modules/openapi-generator/src/main/resources/csharp-netcore/ClientUtils.mustache
index 59684096e76e..8de1caf4bfa4 100644
--- a/modules/openapi-generator/src/main/resources/csharp-netcore/ClientUtils.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp-netcore/ClientUtils.mustache
@@ -116,6 +116,16 @@ namespace {{packageName}}.Client
             return Convert.ToString(obj, CultureInfo.InvariantCulture);
         }
 
+        /// <summary>
+        /// Serializes the given object when not null. Otherwise return null.
+        /// </summary>
+        /// <param name="obj">The object to serialize.</param>
+        /// <returns>Serialized string.</returns>
+        public static string Serialize(object obj)
+        {
+            return obj != null ? Newtonsoft.Json.JsonConvert.SerializeObject(obj) : null;
+        }
+
         /// <summary>
         /// Encode string in base64 format.
         /// </summary>
diff --git a/modules/openapi-generator/src/main/resources/csharp-netcore/api.mustache b/modules/openapi-generator/src/main/resources/csharp-netcore/api.mustache
index 9a9a98cac3ec..99d24d2aaa04 100644
--- a/modules/openapi-generator/src/main/resources/csharp-netcore/api.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp-netcore/api.mustache
@@ -371,7 +371,7 @@ namespace {{packageName}}.{{apiPackage}}
             {{/isArray}}
             {{/isFile}}
             {{^isFile}}
-            localVarRequestOptions.FormParameters.Add("{{baseName}}", {{packageName}}.Client.ClientUtils.ParameterToString({{paramName}})); // form parameter
+            localVarRequestOptions.FormParameters.Add("{{baseName}}", {{packageName}}.Client.ClientUtils.{{#isPrimitiveType}}ParameterToString{{/isPrimitiveType}}{{^isPrimitiveType}}Serialize{{/isPrimitiveType}}({{paramName}})); // form parameter
             {{/isFile}}
             {{/required}}
             {{^required}}
diff --git a/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Api/MultipartApi.cs b/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Api/MultipartApi.cs
index 1c160451c536..a15b1e7c1196 100644
--- a/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Api/MultipartApi.cs
+++ b/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Api/MultipartApi.cs
@@ -502,7 +502,7 @@ namespace Org.OpenAPITools.Api
                 localVarRequestOptions.HeaderParameters.Add("Accept", localVarAccept);
             }
 
-            localVarRequestOptions.FormParameters.Add("status", Org.OpenAPITools.Client.ClientUtils.ParameterToString(status)); // form parameter
+            localVarRequestOptions.FormParameters.Add("status", Org.OpenAPITools.Client.ClientUtils.Serialize(status)); // form parameter
             if (marker != null)
             {
                 localVarRequestOptions.FormParameters.Add("marker", Org.OpenAPITools.Client.ClientUtils.ParameterToString(marker)); // form parameter
diff --git a/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/ClientUtils.cs
index f287a97a0225..3760fe4455b5 100644
--- a/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -120,6 +120,16 @@ namespace Org.OpenAPITools.Client
             return Convert.ToString(obj, CultureInfo.InvariantCulture);
         }
 
+        /// <summary>
+        /// Serializes the given object when not null. Otherwise return null.
+        /// </summary>
+        /// <param name="obj">The object to serialize.</param>
+        /// <returns>Serialized string.</returns>
+        public static string Serialize(object obj)
+        {
+            return obj != null ? Newtonsoft.Json.JsonConvert.SerializeObject(obj) : null;
+        }
+
         /// <summary>
         /// Encode string in base64 format.
         /// </summary>
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/ClientUtils.cs
index dcc97c295e00..e499a7728e4a 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -120,6 +120,16 @@ namespace Org.OpenAPITools.Client
             return Convert.ToString(obj, CultureInfo.InvariantCulture);
         }
 
+        /// <summary>
+        /// Serializes the given object when not null. Otherwise return null.
+        /// </summary>
+        /// <param name="obj">The object to serialize.</param>
+        /// <returns>Serialized string.</returns>
+        public static string Serialize(object obj)
+        {
+            return obj != null ? Newtonsoft.Json.JsonConvert.SerializeObject(obj) : null;
+        }
+
         /// <summary>
         /// Encode string in base64 format.
         /// </summary>
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/ClientUtils.cs
index dcc97c295e00..e499a7728e4a 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -120,6 +120,16 @@ namespace Org.OpenAPITools.Client
             return Convert.ToString(obj, CultureInfo.InvariantCulture);
         }
 
+        /// <summary>
+        /// Serializes the given object when not null. Otherwise return null.
+        /// </summary>
+        /// <param name="obj">The object to serialize.</param>
+        /// <returns>Serialized string.</returns>
+        public static string Serialize(object obj)
+        {
+            return obj != null ? Newtonsoft.Json.JsonConvert.SerializeObject(obj) : null;
+        }
+
         /// <summary>
         /// Encode string in base64 format.
         /// </summary>
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/ClientUtils.cs
index dcc97c295e00..e499a7728e4a 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -120,6 +120,16 @@ namespace Org.OpenAPITools.Client
             return Convert.ToString(obj, CultureInfo.InvariantCulture);
         }
 
+        /// <summary>
+        /// Serializes the given object when not null. Otherwise return null.
+        /// </summary>
+        /// <param name="obj">The object to serialize.</param>
+        /// <returns>Serialized string.</returns>
+        public static string Serialize(object obj)
+        {
+            return obj != null ? Newtonsoft.Json.JsonConvert.SerializeObject(obj) : null;
+        }
+
         /// <summary>
         /// Encode string in base64 format.
         /// </summary>
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/ClientUtils.cs
index dcc97c295e00..e499a7728e4a 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -120,6 +120,16 @@ namespace Org.OpenAPITools.Client
             return Convert.ToString(obj, CultureInfo.InvariantCulture);
         }
 
+        /// <summary>
+        /// Serializes the given object when not null. Otherwise return null.
+        /// </summary>
+        /// <param name="obj">The object to serialize.</param>
+        /// <returns>Serialized string.</returns>
+        public static string Serialize(object obj)
+        {
+            return obj != null ? Newtonsoft.Json.JsonConvert.SerializeObject(obj) : null;
+        }
+
         /// <summary>
         /// Encode string in base64 format.
         /// </summary>
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/ClientUtils.cs
index dcc97c295e00..e499a7728e4a 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -120,6 +120,16 @@ namespace Org.OpenAPITools.Client
             return Convert.ToString(obj, CultureInfo.InvariantCulture);
         }
 
+        /// <summary>
+        /// Serializes the given object when not null. Otherwise return null.
+        /// </summary>
+        /// <param name="obj">The object to serialize.</param>
+        /// <returns>Serialized string.</returns>
+        public static string Serialize(object obj)
+        {
+            return obj != null ? Newtonsoft.Json.JsonConvert.SerializeObject(obj) : null;
+        }
+
         /// <summary>
         /// Encode string in base64 format.
         /// </summary>
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/ClientUtils.cs
index dcc97c295e00..e499a7728e4a 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -120,6 +120,16 @@ namespace Org.OpenAPITools.Client
             return Convert.ToString(obj, CultureInfo.InvariantCulture);
         }
 
+        /// <summary>
+        /// Serializes the given object when not null. Otherwise return null.
+        /// </summary>
+        /// <param name="obj">The object to serialize.</param>
+        /// <returns>Serialized string.</returns>
+        public static string Serialize(object obj)
+        {
+            return obj != null ? Newtonsoft.Json.JsonConvert.SerializeObject(obj) : null;
+        }
+
         /// <summary>
         /// Encode string in base64 format.
         /// </summary>
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/ClientUtils.cs b/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/ClientUtils.cs
index 494b55f85260..21fe44c8dfa4 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/ClientUtils.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/ClientUtils.cs
@@ -120,6 +120,16 @@ namespace Org.OpenAPITools.Client
             return Convert.ToString(obj, CultureInfo.InvariantCulture);
         }
 
+        /// <summary>
+        /// Serializes the given object when not null. Otherwise return null.
+        /// </summary>
+        /// <param name="obj">The object to serialize.</param>
+        /// <returns>Serialized string.</returns>
+        public static string Serialize(object obj)
+        {
+            return obj != null ? Newtonsoft.Json.JsonConvert.SerializeObject(obj) : null;
+        }
+
         /// <summary>
         /// Encode string in base64 format.
         /// </summary>