Wait, Heiko, I hope you get this message before you spend your time on
this!
First of all, I confirmed what Dave said: the Oracle Toplink package
was indeed sending every single NULL with an SQL type of VARCHAR. I
downloaded the postgresql JDBC source code and slowly traced what was
going on, and put in the necessary printlns to see what was being
sent. Garbage in, garbage out.
The good news: the latest version of the Toplink package solves it: it
correctly switches the type of the NULL based on the real type of the
field.
I thank you very much for attempting to help me, and I hope your
problem also gets solved similarly thru an upgrade. It is frustrating
building off of buggy software, but on the other hand, these are
enormously useful packages that people are putting out for free, so I
can't complain. Just gotta try and get some uninterrupted sleep now...
-A