We didn't have a proper black list setup for Linux in Minion in 3.0.4. Please try this development client (3.0.5)
https://cdn.mmoui.com/minion/v3/Mini...5-dev-java.zip. Alternatively if you delete your ~/.minion/minion.xml and restart Minion it should ask you what games you wish Minion to find. Uncheck the games and then it shouldn't scan for any games. Although I'm guessing the Null pointer is happening before the prompt so you will probably need to try 3.0.5.
When you run this Minion will say there is an update. Ignore that and press 'Update Later'. You actually have a newer version (3.0.5) of the client than what the API knows about.
Let me know if this is fixed for you.