@Override
        public boolean addAll(@NonNull Collection<? extends String> c) {
            throw new UnsupportedOperationException("Map.keySet must return a Set which does not support addAll");
        }
Not supported for sets returned by <code>Map.keySet</code>.
netbare-injector/src/main/java/com/github/megatronking/netbare/utils/CaseInsensitiveLinkedMap.java