Cannot create an empty text field

[BeksOmega]

Describe the bug

Text fields do not allow you to delete their text to create an empty text value.

To Reproduce

Steps to reproduce the behavior:

1. Go to the playground.
2. Drag out a block with a text input.
3. Type some text into it, and deselect the field to set the value.
4. Select the field again, and delete the text, then deselect.
5. Observe how the field resets to the previous value you entered, rather than having no text.

Expected behavior

You should be able to delete the text from text input fields.

Additional context

Originally filed here: https://groups.google.com/g/blockly/c/wGzD3uSsZw0/m/nd8G0XbbAgAJ