Fix null exception in PropagateExternalParametersScript.java

[leechristensen]

Added a null check to account for when an address refers to a to a pointer. The screenshots highlight two cases where this occurs in msinfo32.exe on Windows due to MFC/CFG addresses.

[ghidra007]

@leechristensen Did you add the change to use the full package in the print so you don't have to organize imports after uncommenting it?

[leechristensen]

Yep, but happy to change things if wanted. Could split it across a couple lines if wanted or add the import

[ghidra007]

When I review it I'll update to add a define option so that the import is always there.