Add button that loads family and style names from UFO masters. Wrap generate code in a try/except/finally
Add button that loads family and style names from UFO masters.
Wrap generate code in a try/except/finally

So, generating works with the aforementioned RF beta. However, if your designspace document contains glyph masters (as an export of a superpolator document with rules for instance) then some of the instances will not work. Needs an update of MutatorMath in RF.

LettError/designSpaceRoboFontExtension