Error creating shaded jar: null: IllegalArgumentException

Just to sort of pile on, the upgrade to the latest version of the plugin also fixed the issue for me. My problem was that the example I had found used the older version and I wasn't thinking about upgrading it, just getting the configuration to solve my issue. Now I will be more conscientious about finding the latest upgrade plus the new configuration.

I ran into the same issue with version 2.4.3. Upgrading to the latest version of the plugin (currently 3.2.1) took care of it.