code: def visit_union(self, node, visited_children):
      tunion, _, brace, maybe_fields, brace = visited_children
      if not maybe_fields:
          return types.tunion()
      else:
          fields = maybe_fields[0]
          return types.tunion(**dict(fields))
  
imports: from parsimonious import Grammar, NodeVisitor
  from hail.expr.nat import NatVariable
  from .None import types
  from hail.utils.java import unescape_parsable
label_desc: Use image node_id 18 for calling the TypeConstructor obj's underlying member method code with example usage: obj.visit_union(node, visited_children) and returns: types, types