makeOTF error something something something feature file

Trying to export some .otf fonts: very small glyph subset for weight testing, no OTL features specified in Font Info, but getting this error message:

The error messages from makeOTF are a bit opaque. There is a tutorial that explains how to debug this:

Thanks. I dug about in the feature file that was generated in the makeOTF process and it looks like something in the source (inherited from an older TTF that I was working with in FontLab 5) was trying to write a vmtx table entry for the /NULL/ glyph, and that caused some kind of problem. Not more detailed than that, alas.

That is all detail needed. In this case the easiest would be to disable that glyph.
Could you send me the file that I can catch that error directly?

Sorry, this project is in the top secret category, but I’ll see if I can recreate the issue in another file that I can send you. I think it may be affecting other glyphs: that’s just the first one that it hits in the vmtx table entry in the feature file.

In the Plugin Manager, you will find a plug-in called Disguiser that replaces all glyphs with their bounding boxes. Make a duplicate of the .glyphs file, run the filter on all glyphs. And if you need to keep a certain name/wording secret as well, open the file in a text editor and do a search/replace.