2.5.2 Emptying CSS Fallback String in Custom Fonts causes Validation Error and won't save

[ehausen]

You MUST include a clear description of the bug and EXACT steps to reproduce the bug or IT WILL BE CLOSED:

1. Go to Preferences > Custom Fonts and open a already defined font with CSS Fallback
2. Erase the CSS Fallback String and try to save.
3. Observe the Validation Error: IO-TS decoding failed Check browser console for debug information.

Console error.
Type null at path .[0].fontRegistrationData.fallbackString is not assignable to type string (e)

Any other string seems to save fine, but empty will not.

Breakdance version 2.5.2