I was surprised (but not too much) that DB2 ignores the semantics on Null fields for Blobs on JDBC.
Phillip Thurmond has done some tests, and he had to replace ps.setNull by ps.setBinaryStream(null). It seems this has no implications on the other DBs, as the other DBs are also understanding ps.setbinaryStream(nulll).
Because of that, Phillip has submitted a patch where he is changing how we set Null fields on Blobs. It's just a small change but it requires testing on all the other Databases.
Also, Phillip's patch also contains a tested DB2 persistence file.