code: public boolean sendJoinRequest(Address toAddress, boolean withCredentials) {
          if (toAddress == null) {
              toAddress = clusterService.getMasterAddress();
          }
          JoinRequestOp joinRequest = new JoinRequestOp(node.createJoinRequest(withCredentials));
          return nodeEngine.getOperationService().send(joinRequest, toAddress);
      }
docs: Send join request to {@code toAddress}.
  
  @param toAddress       the currently known master address.
  @param withCredentials use cluster credentials
  @return {@code true} if join request was sent successfully, otherwise {@code false}.