Wait until all transferred events have been sent.

async def wait_async(self):
        """
        Wait until all transferred events have been sent.
        """
        if self.error:
            raise self.error
        if not self.running:
            raise ValueError("Unable to send until client has been started.")
        try:
            await self._handler.wait_async()
        except (errors.TokenExpired, errors.AuthenticationException):
            log.info("AsyncSender disconnected due to token error. Attempting reconnect.")
            await self.reconnect_async()
        except (errors.LinkDetach, errors.ConnectionClose) as shutdown:
            if shutdown.action.retry and self.auto_reconnect:
                log.info("AsyncSender detached. Attempting reconnect.")
                await self.reconnect_async()
            else:
                log.info("AsyncSender detached. Shutting down.")
                error = EventHubError(str(shutdown), shutdown)
                await self.close_async(exception=error)
                raise error
        except errors.MessageHandlerError as shutdown:
            if self.auto_reconnect:
                log.info("AsyncSender detached. Attempting reconnect.")
                await self.reconnect_async()
            else:
                log.info("AsyncSender detached. Shutting down.")
                error = EventHubError(str(shutdown), shutdown)
                await self.close_async(exception=error)
                raise error
        except Exception as e:
            log.info("Unexpected error occurred (%r).", e)
            raise EventHubError("Send failed: {}".format(e))