code: private String determineSlotSharingGroup(String specifiedGroup, Collection<Integer> inputIds) {
  		if (specifiedGroup != null) {
  			return specifiedGroup;
  		} else {
  			String inputGroup = null;
  			for (int id: inputIds) {
  				String inputGroupCandidate = streamGraph.getSlotSharingGroup(id);
  				if (inputGroup == null) {
  					inputGroup = inputGroupCandidate;
  				} else if (!inputGroup.equals(inputGroupCandidate)) {
  					return "default";
  				}
  			}
  			return inputGroup == null ? "default" : inputGroup;
  		}
  	}
docs: Determines the slot sharing group for an operation based on the slot sharing group set by
  the user and the slot sharing groups of the inputs.
  
  <p>If the user specifies a group name, this is taken as is. If nothing is specified and
  the input operations all have the same group name then this name is taken. Otherwise the
  default group is chosen.
  
  @param specifiedGroup The group specified by the user.
  @param inputIds The IDs of the input operations.