code: def __parameter_default(self, field):
      
      if field.default:
        if isinstance(field, messages.EnumField):
          return field.default.name
        elif isinstance(field, messages.BooleanField):
          # The Python standard representation of a boolean value causes problems
          # when generating client code.
          return 'true' if field.default else 'false'
        else:
          return str(field.default)
docs: Returns default value of field if it has one.
  
      Args:
        field: A simple field.
  
      Returns:
        The default value of the field, if any exists, with the exception of an
            enum field, which will have its value cast to a string.