Compatibility with OSX

[Willem Rein Oudshoorn]

A few weeks ago a changes was made so that NSText* do not
recognize *nil* values anymore. It throws an exception.

The reasoning was, as far as I recall:

OSX throws an exception and GNUstep should be compatible
and throw an exception too.

However I would like to revert to the previous behaviour.
Throwing an exception in this case makes me write
more code.  Basically all set methods should be guarded
with:  [xxx setValue: y ? y: @""]
to avoid a runtime exception.  

Also, if you, by accident, set a nil value you program crashes.
Personally I think a GUI library should not do this.  
nil is perfectly fine and GNUstep should try to cope with it
as gracefully as it can.  I rather have an empty field
than a crash.

Wim Oudshoorn.