static final class Helper<K, V>
        implements InternalEntryHelper<
            K, V, StrongKeyStrongValueEntry<K, V>, StrongKeyStrongValueSegment<K, V>> {
      private static final Helper<?, ?> INSTANCE = new Helper<>();

      @SuppressWarnings("unchecked")
      static <K, V> Helper<K, V> instance() {
        return (Helper<K, V>) INSTANCE;
      }

      @Override