Small fix for ResourceList.post

Co-authored-by: Suren Khorenyan <surenkhorenyan@gmail.com>

Author: Dmitry Mishanov

flask_combo_jsonapi/resource.py

@@ -185,7 +185,7 @@ def post(self, *args, **kwargs):
         else:
             result = schema.dump(obj)
 
-        if result["data"].get("links", {}).get("self"):
+        if (result["data"] or {}).get("links", {}).get("self"):
             final_result = (result, 201, {"Location": result["data"]["links"]["self"]})
         else:
             final_result = (result, 201)