Two suggestions:
-
Consider asking how to solve your problem (getting users to fill the in the field). The user wizard plugin might be a solution?
-
Move this to Development and ask there. I think that it might be possible with a theme component if the values are in serializer.
For either, change he subject to something like “how can I force users to fill in a custom field when it’s empty”
I don’t have a very good answer, though. 