NPE in Parser.__saveState when accessing rule

[mustajarvi]

I tried just outputting the rule itself to check it's type, but that resulted in a NPE. Example:

object Nullpointer {
  import org.parboiled2._

  class Bar(val input: ParserInput) extends Parser {
    def Digits = rule { oneOrMore(CharPredicate.Digit) }
  }

  def main(args: Array[String]): Unit = {
    println(new Bar("").Digits)
  }
}

Might be a nonsensical use but a NPE is still a bit surprising.

[sirthias]

As an optimization parboiled encodes "rule mismatch" as null. So, in your example, if Digits returns null it means "rule didn't match". This is expected behavior and a consequence of how parboiled currently works.

"Outputting the rule itself" indeed makes no sense.