code: public static byte[] normalizeKey(byte[] keyData) {
          if (keyData == null) {
              return RSG.generate(16).getBytes(StandardCharsets.UTF_8);
          } else {
              return normalizeKey(new String(keyData, StandardCharsets.UTF_8))
                      .getBytes(StandardCharsets.UTF_8);
          }
      }
docs: AES key should be 16 bytes in length.
  
  @param key
  @return