make default parameter overloads binary compatible

Author: CumpsD

src/Microsoft.OpenApi/Extensions/OpenApiSerializableExtensions.cs

@@ -41,6 +41,25 @@ public static void SerializeAsYaml<T>(this T element, Stream stream, OpenApiSpec
             element.Serialize(stream, specVersion, OpenApiFormat.Yaml);
         }
 
+        /// <summary>
+        /// Serializes the <see cref="IOpenApiSerializable"/> to the Open API document using
+        /// the given stream, specification version and the format.
+        /// </summary>
+        /// <typeparam name="T">the <see cref="IOpenApiSerializable"/></typeparam>
+        /// <param name="element">The Open API element.</param>
+        /// <param name="stream">The given stream.</param>
+        /// <param name="specVersion">The Open API specification version.</param>
+        /// <param name="format">The output format (JSON or YAML).</param>
+        public static void Serialize<T>(
+            this T element,
+            Stream stream,
+            OpenApiSpecVersion specVersion,
+            OpenApiFormat format)
+            where T : IOpenApiSerializable
+        {
+            element.Serialize(stream, specVersion, format, null);
+        }
+
         /// <summary>
         /// Serializes the <see cref="IOpenApiSerializable"/> to the Open API document using
         /// the given stream, specification version and the format.
@@ -56,7 +75,7 @@ public static void Serialize<T>(
             Stream stream,
             OpenApiSpecVersion specVersion,
             OpenApiFormat format, 
-            OpenApiWriterSettings settings = null)
+            OpenApiWriterSettings settings)
             where T : IOpenApiSerializable
         {
             if (stream == null)

src/Microsoft.OpenApi/Writers/OpenApiJsonWriter.cs

@@ -10,12 +10,20 @@ namespace Microsoft.OpenApi.Writers
     /// </summary>
     public class OpenApiJsonWriter : OpenApiWriterBase
     {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="OpenApiJsonWriter"/> class.
+        /// </summary>
+        /// <param name="textWriter">The text writer.</param>
+        public OpenApiJsonWriter(TextWriter textWriter) : base(textWriter, null)
+        {
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="OpenApiJsonWriter"/> class.
         /// </summary>
         /// <param name="textWriter">The text writer.</param>
         /// <param name="settings">Settings for controlling how the OpenAPI document will be written out.</param>
-        public OpenApiJsonWriter(TextWriter textWriter, OpenApiWriterSettings settings = null) : base(textWriter, settings)
+        public OpenApiJsonWriter(TextWriter textWriter, OpenApiWriterSettings settings) : base(textWriter, settings)
         {
         }
 

src/Microsoft.OpenApi/Writers/OpenApiWriterBase.cs

@@ -5,7 +5,6 @@
 using System.Collections.Generic;
 using System.IO;
 using Microsoft.OpenApi.Exceptions;
-using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Properties;
 
 namespace Microsoft.OpenApi.Writers

src/Microsoft.OpenApi/Writers/OpenApiYamlWriter.cs

@@ -10,14 +10,21 @@ namespace Microsoft.OpenApi.Writers
     /// </summary>
     public class OpenApiYamlWriter : OpenApiWriterBase
     {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="OpenApiYamlWriter"/> class.
+        /// </summary>
+        /// <param name="textWriter">The text writer.</param>
+        public OpenApiYamlWriter(TextWriter textWriter) : this(textWriter, null)
+        {
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="OpenApiYamlWriter"/> class.
         /// </summary>
         /// <param name="textWriter">The text writer.</param>
         /// <param name="settings"></param>
-        public OpenApiYamlWriter(TextWriter textWriter, OpenApiWriterSettings settings = null) : base(textWriter, settings)
+        public OpenApiYamlWriter(TextWriter textWriter, OpenApiWriterSettings settings) : base(textWriter, settings)
         {
-           
         }
 
         /// <summary>