Fix the bug from the PR

MelbourneDeveloper · MelbourneDeveloper · commit ead38f28fbaa · 2023-04-12T14:36:02.000+10:00
diff --git a/src/RestClient.Net/Client.cs b/src/RestClient.Net/Client.cs
@@ -155,7 +155,11 @@ public Client(
             {
                 //Use a shared instance for serialization. There should be no reason that this is not thread safe. Unless it's not.
                 SerializationAdapter = JsonSerializationAdapter.Instance;
-                DefaultRequestHeaders = DefaultRequestHeaders.WithJsonContentTypeHeader();
+
+                DefaultRequestHeaders =
+                    defaultRequestHeaders == null ? DefaultRequestHeaders.WithJsonContentTypeHeader() :
+                    defaultRequestHeaders.Contains(HeadersExtensions.ContentTypeHeaderName) ?
+                    defaultRequestHeaders : defaultRequestHeaders.WithJsonContentTypeHeader();
             }
             else
             {

Original file line number	Diff line number	Diff line change
`@@ -155,7 +155,11 @@ public Client(`
`155`	`155`	`{`
`156`	`156`	`//Use a shared instance for serialization. There should be no reason that this is not thread safe. Unless it's not.`
`157`	`157`	`SerializationAdapter = JsonSerializationAdapter.Instance;`
`158`		`- DefaultRequestHeaders = DefaultRequestHeaders.WithJsonContentTypeHeader();`
	`158`	`+`
	`159`	`+ DefaultRequestHeaders =`
	`160`	`+ defaultRequestHeaders == null ? DefaultRequestHeaders.WithJsonContentTypeHeader() :`
	`161`	`+ defaultRequestHeaders.Contains(HeadersExtensions.ContentTypeHeaderName) ?`
	`162`	`+ defaultRequestHeaders : defaultRequestHeaders.WithJsonContentTypeHeader();`
`159`	`163`	`}`
`160`	`164`	`else`
`161`	`165`	`{`