code: public void addClientIfNotPresent(DeviceGuiElement device) {
          boolean add = true;
          for (DeviceGuiElement element : clients) {
              if (element != null
                      && element.getName().equals(device.getName())
                      && element.getAddress().equals(device.getAddress())) {
                  add = false; //already in the list
              }
          }
  
          if (add) {
              clients.add(device);
          }
      }
docs: Method to add a client inside the list in a secure way.
  The client is added only if isn't already inside the list.
  
  @param device {@link DeviceGuiElement} to add.