Using "?." and "??" JS operators in action code blocks ?

Hi!

This is more a question rather a bug, is the ES version used by rules execution capped ?

I'm trying to use both optional chaining ?. and nullish coalescing operator ?? but I'm getting errors:

test
  : DEBUG                         -> yy.test?.hello ?? null //Tried with { return yy.test?.hello ?? null } too
  ;

error: Uncaught (in promise) Error: Could not parse jison grammar
Error:
production rule action code block does not compile: Line 45: Unexpected token .

  Erroneous area:
45:   : DEBUG                         -> yy.test?.hello ?? null
^^....................................^^^^^^^^^^^^^^^^^^^^^^^^^

Thanks for your work 🙂

GerHobbelt / jison

Using "?." and "??" JS operators in action code blocks ? #63