Java: Check null pointers

[Alexandre Petit-Bianco]

Andrew Haley writes:

> I want to put it into the trunk now.

I think I see a `make check' regression but I can't reproduce it. It's
the second time today I witness this with `make check.'

I will investigate, meanwhile, I didn't see any other regression but
this one, so I guess the patch is good for the trunk.

Thanks!

./A