6ffefd8e-a018-e811-bbf9-60f67727d806 should be recognized as a valid GUID when used as a parameter. This GUID was generated by SQL Server and should regarded as valid. In utils.js in the method ...
If there is a guid in the clipboard then it will put a formatted guid in the clipboard. If there is a 0 or f in clipboard then it will replace it with a guid that's all 0 or f.
If you are asking “GUI-what?”, not to worry, you aren’t alone. A GUID is a Globally Unique Identifier that helps manage the relational data in the Common Data Service for Apps and SQL Server.