<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _set_client(self):
 """Set client property if not set."""

        if self._client is None:
            if mongo_proxy:
                self._client = mongo_proxy.MongoProxy(
                    pymongo.MongoClient(self.connection_string),
                    logger=LOG)
            else:
                LOG.warning("MongoDBProxy not imported. AutoReconnect "
                            "is not enabled.")
                self._client = mongo_proxy.MongoProxy(
                    pymongo.MongoClient(self.connection_string),
                    logger=LOG)
            LOG.debug("Created new connection to MongoDB: %s",
                      self.safe_connection_string)