Fireballs crashing my minecraft

Fireball crashed my minecraft

What I expected to happen was...:
I thought that when I used the summon command to summon a fireball a fireball whould have been summoned.

What actually happened was...:
When I activated the command block my minecraft crashed, now I can't get into my world because it always crashes when I log into it.

Steps to Reproduce:
1. Summon a fireball using a command block and let it float in the air