derefLocationSet = new HashSet<Location>();
derefLocationSet = Collections.EMPTY_SET;
	public Set<Location> getUnconditionalDerefLocationSet(ValueNumber vn) {		Set<Location> derefLocationSet = derefLocationSetMap.get(vn);		if (derefLocationSet == null ) {			derefLocationSet = new HashSet<Location>();		}		return derefLocationSet;	}