code: public static Collection<String> getPropertyNames(
  			Collection<Channel> channels) {
  		Collection<String> propertyNames = new HashSet<String>();
  		for (Channel channel : channels) {
  			propertyNames.addAll(getPropertyNames(channel));
  		}
  		return propertyNames;
  	}
docs: Return a union of property names associated with channels
  
  @param channels - list of channels
  @return a set of all unique property names associated with atleast one or
  more channel in channels