Commands cannot effect an entity's custom name

Entity names cannot be created or modified using the /summon or /data commands. The command returns "Unable to summon entity" or "An unexpected error occurred trying to execute that command"

How to reproduce:
Attempt to summon an entity using

/summon bat ~ ~ ~ {CustomName:"Gun",NoAI:1b,Silent:1b}

Attempt to rename an entity using

/data merge entity @e[type=bat,limit=1] {CustomName:"Gun"}