docs: protected static String letterify(String letterString) {
          StringBuffer sb = new StringBuffer();
          for (int i = 0; i < letterString.length(); i++) {
              if (letterString.charAt(i) == '?') {
                  sb.append((char) (97 + RandomUtils.nextInt(26))); // a-z
              } else {
                  sb.append(letterString.charAt(i));
              }
          }
  
          return sb.toString();
      }