code: public void unblockUser(DomainBareJid mucLightService, Jid userJid)
              throws NoResponseException, XMPPErrorException, NotConnectedException, InterruptedException {
          HashMap<Jid, Boolean> users = new HashMap<>();
          users.put(userJid, true);
          sendUnblockUsers(mucLightService, users);
      }
docs: Unblock a user.
  
  @param mucLightService
  @param userJid
  @throws NoResponseException
  @throws XMPPErrorException
  @throws NotConnectedException
  @throws InterruptedException