code: def visit_Opt(self, item: Opt) -> Set[str]:
      return self.visit(item.node)
  
imports: import argparse
  import pprint
  import sys
  from typing import Dict, Set
  from pegen.build import build_parser
  from pegen.grammar import Alt, Cut, Gather, GrammarVisitor, Group, Lookahead, NamedItem, NameLeaf, NegativeLookahead, Opt, Repeat0, Repeat1, Rhs, Rule, StringLeaf
  from pegen.parser_generator import compute_nullables
label_desc: Use image node_id 9 for calling the FirstSetCalculator obj's underlying member method code with example usage: obj.visit_Opt(item) and returns: self