It's ok for Object types, but how about primitive types?
Primitives can't be null (see the Java Language Specification); instead use a primitive wrapper (e.g., java.lang.Integer).
We're having the same problems here and our applications have to be deployed on multiple application servers.
It seems that WebLogic already takes care of this and returns e.g. 0.0 when retrieving a null value on a double field from the database. Why doesn't JBoss also take care of this?