Minecraft crashes when i use some comands

What I expected to happen was...:
the command would work and everything would be fine.

What actually happened was...:
I entered in the command and it went in fine but when I clicked done it crashed my minecraft.

Steps to Reproduce:
1. get a command block in game
2.type in a very long command mabey like 1,000,000 characters worth
3. then after writing it hit the done button and minecraft crashes.