<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 async def close(self) -> None: """ Explicit exit. Closes pool. For use when keeping pool open across multiple calls. """


        LOGGER.debug('NodePool.close >>>')

        if not self.handle:
            LOGGER.warning('Abstaining from closing pool %s: already closed', self.name)
        else:
            await pool.close_pool_ledger(self.handle)
        self._handle = None

        LOGGER.debug('NodePool.close <<<')