In 1.12.2, you could put an empty string in an anvil to remove a custom name. This is no longer possible.
Steps to reproduce:
Rename any item with an anvil
Put the named item back into the anvil and delete the entire name
Rather than the default name, a single character from the custom name will remain.
If this is intended behavior, MC-113869 can be closed as well because it involves removing a custom name.
Linked issues
Comments

Ah, sorry. Didn't see that one.