[developers] Unfilled feature structures sometimes causing error.

[Ann Copestake]

The menu option `Unfilled feature structure' gives an error `Second argument 
of check-type-values() cannot be nil' when chosen on some (but not all) nodes 
of a Parse tree in the LKB/CLIM interface.  e.g. Parsing `Tom ate because of 
his hunger.' this happens for the uppermost VP of the correct parse.  This is 
with the latest LKB and ERG (i.e., the main repositories, not LOGON)