bug: Clearing lexeme fields leads to exception notice

[laineyhm]

Describe the bug
When you take out the lexeme forms from a project that was imported through LIFT, you get the following notice:

even though when you click out of the notice, you can go on as usual.

To Reproduce
Steps to reproduce the behavior:

1. In FLEx, make a project, can have as few as 2 entries. Fill in the lexeme form and the gloss and/or definition in the sense for these entries.
2. Export the project as a LIFT file of the Full Lexicon.
3. In Language Forge, create a new non-send receive project. Name it and then import entries from LIFT file.
4. In the Language Forge editor, delete the entries to the "word" fields.
5. After a moment, you will receive the exception notice.
6. Click out of the exception notice, and observe that you can edit as normal.

Expected behavior
Although L:IFT imports are not a recommended way to go anymore, the expected behavior in this scenario is to be able to remove the data in word fields without a problem or a notice of a problem. In a project that's created in Language Forge or created through send/receive, this exception does not occur.

Additional context
This issue was reported by Ken Zook on March 14, 2023.