docs: public static String getRandomAlphaNumeric(int length) {
          if (length <= 0) {
              return "";
          }
  
          Random r = getRandom();
  
          StringBuffer result = new StringBuffer(length);
  
          for (int i = 0; i < length; i++) {
              int n = r.nextInt(alphaNumChars.length);
              result.append(alphaNumChars[n]);
          }
  
          return result.toString();
      }