Worldborder danage error

When you do '/worldborder damage time' or '/worldborder damage distance' the message 'An unknow erroroccured while attempting to preform this command'

What I expected to happen was...:
I didn't realy know as I was experimenting with the snapshot

What actually happened was...:
The above error message came up

Steps to Reproduce:
1. Start a customized world
2. Do '/worldborder damage time'
3. Then do '/worldborder damage distance'