My minecraft is bugging out when i go onto servers and world's

Put the summary of the bug you're having here

*What I expected to happen was to go into mineplex the server
Describe what you thought should happen here

*What actually happened was it said "java.lang.NullPointer:group
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2.log on to minecraft
3.go into a flat woruld
4.eat a notch apple
5.log on to a server
6. thats it