Wither can't be summoned with a CustomName and can only be named with a name tag. Also, seprate bug in 1.13, but anvils dont work in creative.

Put the summary of the bug you're having here

What I expected to happen was...:
That the wither woud be summoned in with a custom name

What actually happened was...:
Nothing, and the game gave me errors, and I had to give myself a named name tag.

Steps to Reproduce:
1. Play in 1.13 or 1.13.2
2. try to do /summon minecraft:wither ~ ~ ~

{CustomName:"Dinnerbone",Invul:1000,NoAI:1}

3. try to use an anvil in creative to rename a name tag when that command doesnt work

(neither thing will)