code: private void sendEmptyRequest() {
          assertUnlocked();
          // Send an empty request
          LOG.finest("Sending empty request");
          try {
              send(ComposableBody.builder().build());
          } catch (BOSHException boshx) {
              dispose(boshx);
          }
      }
docs: Sends an empty request to maintain session requirements.  If a request
  is sent within a reasonable time window, the empty request transmission
  will be cancelled.