code: public static List<Tag<String>> tagValuesToString(List<? extends Tag<?>> tags) {
      return Lists.transform(tags, new Function<Tag<?>, Tag<String>>() {
        @Nullable @Override public Tag<String> apply(Tag<?> input) {
          return input == null ? null : Tag.tagValueToString(input);
        }
      });
    }
docs: Converts a {@link List} of wildcard {@link Tag}s to a {@link List} of {@link String} {@link Tag}s.
  
  @param tags a {@link List} of {@link Tag}s that should be converted to {@link Tag}s with value of type {@link String}
  
  @return a {@link List} of {@link Tag}s
  
  @see #tagValueToString(Tag)