Message4351

Debugging the code, it happens that
PyStringMap.__setitem__(String key, PyObject newValue)
on the "locals" object of PythonInterpreter is called with the arguments

key = "j"
newValue = null

As far as I know, setting "j" to null shouldn't happen; a null object in
Jython is PyNone, which is not a Java null.

Checking whether an object exists in the namespace is done by asking for
its key and seeing that the returned value is not null. Therefore,
setting "j" to null provokes the NameError later on.