private Set<Component> unionComponentSet(Set<Component> set1, Set<Component> set2) {
if (set1 == null && set2 == null) return Collections.emptySet();
if (set1 == null) return set2;
if (set2 == null) return set1;
Set<Component> set = new HashSet<Component>(set1.size() + set2.size());
set.addAll(set1);
set.addAll(set2);
return set;
}
/** Always returns the empty set */
@Override
public Set<java.util.Map.Entry<K, K>> entrySet() {
return Collections.emptySet();
}