code: def default(self, statement: Statement) -> Optional[bool]:
          
          if self.default_to_shell:
              if 'shell' not in self.exclude_from_history:
                  self.history.append(statement)
  
              return self.do_shell(statement.command_and_args)
          else:
              err_msg = self.default_error.format(statement.command)
              self.decolorized_write(sys.stderr, "{}\n".format(err_msg))
docs: Executed when the command given isn't a recognized command implemented by a do_* method.
  
          :param statement: Statement object with parsed input