If we're compiling a generator (or coroutine etc.) the new function assumes (without asserting) that entryblock is not NULL. But evidently it could be, since below on line 6690 there's a check whether it could be. I don't know how it could be NULL - that would mean there's no code in the function at all, but it seems there's code above that always adds at least one instruction (RETURN_VALUE on line 6668). So maybe the check for entryblock == NULL below can be replaced by an assert? (I'd place that assert right underneath the for-loop above on lines 6683-6686.

entryblock cannot be NULL. I'll add the assert.