Cannot export a UFO

OS X 10.11.1, G2 2.1.1 [807]

I try and export a font I finished months ago as a UFO and get this error message:

“Something went wrong while exporting: *** -[__NSArrayM insertObject:atIndex:]: object cannot be nil”.

It exports just fine as an OTF font. It doesn’t cause Glyphs to crash, so not Crash Report.

Can you send me the .glyphs file?

I will send it soon.