code: public static <K, V1, V2> Maps.EntryTransformer<K, V1, V2> valueTransformer(
        final Function<? super V1, V2> valueFunction) {
      checkNotNull(valueFunction);
      return new Maps.EntryTransformer<K, V1, V2>() {
        @Override
        public V2 transformEntry(final K key, final V1 value) {
          return valueFunction.apply(value);
        }
      };
    }
docs: Creates a {@link com.google.common.collect.Maps.EntryTransformer} which applies the supplied
  {@link Function} to map entry values.