code: @Override
      public void invoke(String method, IPendingServiceCallback callback) {
          log.debug("invoke method: {} params {} callback {}", new Object[] { method, callback });
          // get it from the conn manager
          if (conn != null) {
              conn.invoke(method, callback);
          } else {
              log.info("Connection was null");
              PendingCall result = new PendingCall(method);
              result.setStatus(Call.STATUS_NOT_CONNECTED);
              callback.resultReceived(result);
          }
      }
docs: Invoke a method on the server.
  
  @param method
  Method name
  @param callback
  Callback handler