code: public Boolean isSubscribed(String channel) {
  		Boolean result = null;
  
  		/*
  		 * Sanity checks
  		 */
  		if (!isConnected) {
  			raiseOrtcEvent(EventEnum.OnException, this,
  					new OrtcNotConnectedException());
  		} else if (Strings.isNullOrEmpty(channel)) {
  			raiseOrtcEvent(EventEnum.OnException, this,
  					new OrtcEmptyFieldException("Channel"));
  		} else if (!Strings.ortcIsValidInput(channel)) {
  			raiseOrtcEvent(EventEnum.OnException, this,
  					new OrtcInvalidCharactersException("Channel"));
  		} else {
  			ChannelSubscription subscribedChannel = subscribedChannels
  					.get(channel);
  			result = subscribedChannel != null
  					&& subscribedChannel.isSubscribed();
  		}
  
  		return result;
  	}
docs: Indicates if the channel is subscribed
  
  @param channel
  Channel to check
  @return boolean True if the channel is subscribed otherwise false