code: public static <K, V> Map.Entry<K, V> immutableEntry(K key, V value) {
        return new ImmutableEntry<>(key, value);
     }
docs: Wraps a key and value with an immutable {@link Map.Entry}}. There is no copying involved.
  
  @param key the key to wrap.
  @param value the value to wrap.
  @return an immutable {@link Map.Entry}} wrapper that delegates to the original mapping.