The bug

When renaming an item in an anvil and emptying the text field (e.g. using the backspace (←) or Del key) the name of the result item is not updated. Instead it uses the text which was last in the text field before it was emptied.

Expected would be that when emptying the text field:

• if the item has a custom name, the custom name was removed (similar to the current behavior when using only spaces as name)
• if the item has no custom name, no result item is shown

Reproduction steps (single backspace)

1. Place a stone block in an anvil
2. Backspace until the text field is empty
3. Look at the output item
   It is named "S" and can be taken out
   

Reproduction steps (Ctrl + backspace)

1. Place a stone block in an anvil
2. Backspace once
3. Ctrl + backspace (the text field is now empty)
4. Look at the output item
   It is named "Ston" and can be taken out
   

Workaround for removing custom name

Currently a custom item name can be removed by only using spaces in the new name. However, due to MC-125046 the item does not stack with other non-renamed items.

Code analysis

Mojang names

net.minecraft.client.gui.screens.inventory.AnvilScreen.onNameChanged(String) returns if the new name is empty.