docs: def _discard_config(self):
          """Set candidate_cfg to current running-config. Erase the merge_cfg file."""
          discard_candidate = "copy running-config {}".format(
              self._gen_full_path(self.candidate_cfg)
          )
          discard_merge = "copy null: {}".format(self._gen_full_path(self.merge_cfg))
          self.device.send_command_expect(discard_candidate)
          self.device.send_command_expect(discard_merge)