It's possible to break trigger wizard form by following these steps:

1. Type in an expression and click "And" or "Or" so that it is added in the keyword table.
2. Try to save form and get a natural error. So far so good.
3. Press "Add" so that the keyword is added to the expression table below.
4. Type in another expression and press "And" or "Or".
5. Press "Add" again to add it to the expression table.
6. Experience the JS error:
   TypeError: key_tr is null

Bug was introduced in 2.4