Calling serverError with a clientError status code (4xx) means it will
automatically default to Internal Server Error (500) which is in the
server error status code range (5xx). That is undesirable.
Now we have to fix any code in the core which directly uses the Fave class
or any other favorite stuff, since it is pluginised and thus might not be
available on some installations.
Mikael Nordfeldth