docs: public static @CheckForNull String resolveOrNull(User u, String avatarSize) {
          Matcher matcher = iconSizeRegex.matcher(avatarSize);
          if (matcher.matches() && matcher.groupCount() == 2) {
              int width = Integer.parseInt(matcher.group(1));
              int height = Integer.parseInt(matcher.group(2));
              for (UserAvatarResolver r : all()) {
                  String name = r.findAvatarFor(u, width, height);
                  if(name!=null) return name;
              }
          } else {
              LOGGER.warning(String.format("Could not split up the avatar size (%s) into a width and height.", avatarSize));
          }
  
          return null;
      }