This behaviour should now be possible - to allow for setups where automatic creation of the default world_nether is not desired (say, if a separate "Nether" world is created). This is only possible when allow-nether=false but NetherPortals currently insists on this requirement.

It actually doesn't insist, it just yells at you. Now that Git has a way for me to see all my issues in one panel, this issue cropped up again. Will fix.