modV hangs / skips / regular hickups when editing tween values

[HorstBaerbel]

Operating system and application version

• OS: Fedora
• Version 3.29.1

Describe the bug
When editing tween values modV sometimes hangs. It seems to happen when the values written to the tween field are not valid JavaScript expressions. It seems to be especially bad when you cut (CTRL+A, CTRL+X) the whole tween values. modV then automatically adds a "[]". Deleting that seems to invoke that hickup behaviour

To Reproduce
Steps to reproduce the behavior:

1. Go to Tweeing, add values
2. Edit values to be faulty JS expressions
3. Leave tweening input field
   OR
4. Go to Tweeing, add values
5. Delete all expressions by cutting them
6. Leave tweening input field -> "[]" gets added
7. Delete "[]"

Expected behavior
No hickups in modV. Possibly an error message for the values, see #886