I can't join multiplayer servers

Put the summary of the bug you're having here

What I expected to happen was...:
I would join the multiplayer server normally

What actually happened was...:
I couldn't log in, and a screen that showed java.lang.nullpointerexeption popped up and it said it failed to join the server

Steps to Reproduce:
1. I don't know, it just happened to me
2. ...
3. ...