Snapshot 18w50a - Realms

While playing on snapshot 18w50a, if you click on 'realms', it instantly crashes the game.

What I expected to happen was...:
It would open the 'realms' tab.

What actually happened was...:
Crashed the game.

Steps to Reproduce:
1. Load up snapshot 18w50a
2. Click on the 'realms' tab.