feat: Added nullable enable to OpenApiMediaType.

Author: HavenDV

src/Microsoft.OpenApi/Models/OpenApiMediaType.cs

@@ -9,19 +9,21 @@
 using Microsoft.OpenApi.Interfaces;
 using Microsoft.OpenApi.Writers;
 
+#nullable enable
+
 namespace Microsoft.OpenApi.Models
 {
     /// <summary>
     /// Media Type Object.
     /// </summary>
     public class OpenApiMediaType : IOpenApiSerializable, IOpenApiExtensible
     {
-        private JsonSchema _schema;
+        private JsonSchema? _schema;
 
         /// <summary>
         /// The schema defining the type used for the request body.
         /// </summary>
-        public virtual JsonSchema Schema
+        public virtual JsonSchema? Schema
         {
             get => _schema;
             set => _schema = value;
@@ -31,26 +33,26 @@ public virtual JsonSchema Schema
         /// Example of the media type.
         /// The example object SHOULD be in the correct format as specified by the media type.
         /// </summary>
-        public OpenApiAny Example { get; set; }
+        public OpenApiAny? Example { get; set; }
 
         /// <summary>
         /// Examples of the media type.
         /// Each example object SHOULD match the media type and specified schema if present.
         /// </summary>
-        public IDictionary<string, OpenApiExample> Examples { get; set; } = new Dictionary<string, OpenApiExample>();
+        public IDictionary<string, OpenApiExample>? Examples { get; set; } = new Dictionary<string, OpenApiExample>();
 
         /// <summary>
         /// A map between a property name and its encoding information.
         /// The key, being the property name, MUST exist in the schema as a property.
         /// The encoding object SHALL only apply to requestBody objects
         /// when the media type is multipart or application/x-www-form-urlencoded.
         /// </summary>
-        public IDictionary<string, OpenApiEncoding> Encoding { get; set; } = new Dictionary<string, OpenApiEncoding>();
+        public IDictionary<string, OpenApiEncoding>? Encoding { get; set; } = new Dictionary<string, OpenApiEncoding>();
 
         /// <summary>
         /// Serialize <see cref="OpenApiExternalDocs"/> to Open Api v3.0.
         /// </summary>
-        public IDictionary<string, IOpenApiExtension> Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
 
         /// <summary>
         /// Parameterless constructor
@@ -60,7 +62,7 @@ public OpenApiMediaType() { }
         /// <summary>
         /// Initializes a copy of an <see cref="OpenApiMediaType"/> object
         /// </summary>
-        public OpenApiMediaType(OpenApiMediaType mediaType)
+        public OpenApiMediaType(OpenApiMediaType? mediaType)
         {
             Schema = mediaType?.Schema != null ? JsonNodeCloneHelper.CloneJsonSchema(mediaType.Schema) : null;
             Example = mediaType?.Example != null ? JsonNodeCloneHelper.Clone(mediaType.Example) : null;