While searching, non existent content types were simply ignored, leading to the situation, that the search wasn't restricted to any content type at all. As this behavior led to bigger result set than expected and may hide bugs on the client side, a content type validation was introduced. Whenever an invalid, non existent content type is given, headless will respond with one GraphQL error message per invalid content type.

This change is classified 'breaking', as a client might have used invalid content types without recognizing them as errors. If this is this case, the new behavior will break the client!

(CMS-17298)