I'm using a custom format in the view screen as well as a lookup against a table in the edit screen.
However, the custom format seems to be being skipped when the value is null (e.g. if I set my custom format to be $value='zzz'; for the null values the return is still blank?)
This is with 4.2 build 379
I'm just about to go and look at the codepath to see why this would be.