public String apply(String input) {
          return new String(BaseEncoding.base64().decode(input), UTF_8);
        }
      };

  private static final EntryTransformer<String, String, String> DECODE_ENTRY_TRANSFORMER =
      new EntryTransformer<String, String, String>() {
        @Override
        public String transformEntry(String key, String value) {
          return DECODE_FUNCTION.apply(value);
        }

          @Override
          public String apply(String value) {
            return Ascii.toLowerCase(value);
          }
        };

    static final EntryTransformer<String, String, String> ENTRY_TRANSFORMER =
        new EntryTransformer<String, String, String>() {
          @Override
          public String transformEntry(String key, String value) {
            return Ascii.toLowerCase(value);
          }

  }

  @GwtIncompatible // untested
  public void testTransformEntries() {
    SetMultimap<String, Integer> multimap = ImmutableSetMultimap.of("a", 1, "a", 4, "b", -6);
    EntryTransformer<String, Integer, String> transformer =
        new EntryTransformer<String, Integer, String>() {
          @Override
          public String transformEntry(String key, Integer value) {
            return (value >= 0) ? key : "no" + key;
          }

          @Override
          public String apply(String value) {
            return Ascii.toLowerCase(value);
          }
        };

    static final EntryTransformer<String, String, String> ENTRY_TRANSFORMER =
        new EntryTransformer<String, String, String>() {
          @Override
          public String transformEntry(String key, String value) {
            return Ascii.toLowerCase(value);
          }