code: @CheckReturnValue
      public ChannelAction setTopic(String topic)
      {
          if (type != ChannelType.TEXT)
              throw new UnsupportedOperationException("Can only set the topic for a TextChannel!");
          if (topic != null && topic.length() > 1024)
              throw new IllegalArgumentException("Channel Topic must not be greater than 1024 in length!");
          this.topic = topic;
          return this;
      }
docs: Sets the topic for the new TextChannel
  
  @param  topic
  The topic for the new Channel (max 1024 chars)
  
  @throws UnsupportedOperationException
  If this ChannelAction is not for a TextChannel
  @throws IllegalArgumentException
  If the provided topic is longer than 1024 chars
  
  @return The current ChannelAction, for chaining convenience