code: @Override
      public void register(Object listener)
      {
          if (!(listener instanceof EventListener))
          {
              throw new IllegalArgumentException("Listener must implement EventListener");
          }
          listeners.add(((EventListener) listener));
      }
docs: {@inheritDoc}
  
  @throws IllegalArgumentException
  If the provided listener does not implement {@link net.dv8tion.jda.core.hooks.EventListener EventListener}