Update: The error has something to do with the spellsheet. I just removed it and exporting worked.
Update 2: It also only occurs with a spell sheet that has the "with text lines" option.
No matter if there is something written in any box on the spell sheet or not, a spell sheet without text lines works flawlessly, but any of the other two options with text lines gives the stated error.
Sadly, when generating a spell sheet to be filled with spells it always will give one with text lines.
In other words:
Not Working: https://pastebin.com/b5Xj2n6M
Working: https://pastebin.com/CntXjvXZ
Nice sleuthing!
If you have a character sheet with a few spells and a sheet with lines, does it work with v1.0.1? You'll probably get a lot of warnings about spells not being found when it encounters the lines, but it should finish exporting after that.
At any rate, I'm going to let the spell creator ignore those lines starting from v1.0.2. I just did some testing myself with 100+ spells and an empty spell sheet with lines and it exported the character fine after the code changes.