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:

1. Rename any item with an anvil
2. 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.