formula: split brain hinders saving

[cnrdh]

Red tab => ERROR, but 0 invalid fields:

[cnrdh]

The trouble in this particular case is that @language seems to be "nn", but it's really null.
The "nn" stems from the default value. The allowed types was ["string", "null"] and the field was set to required.

[cnrdh]

Possiuble to not set default except for empty documents?