I’m following this as I’m having the same problem.
Didn’t you say that Null’s are not a problem in general?
Will definitely check my model for Nulls now 
I’m trying to figure out the root cause for the same undefined error which only occured after the latest Shapediver viewer update (around May 4, I think) on a model, that uploaded fine just before that update. Exact same model, no changes in between.