Added empty schema to body parameters in V2

Author: darrelmiller

src/Microsoft.OpenApi/Models/OpenApiOperation.cs

@@ -247,7 +247,7 @@ public void SerializeAsV2(IOpenApiWriter writer)
                         // V2 spec actually allows the body to have custom name.
                         // Our library does not support this at the moment.
                         Name = "body",
-                        Schema = content?.Schema,
+                        Schema = content?.Schema ?? new OpenApiSchema(),
                         Required = RequestBody.Required
                     };