code: public static byte[] addressStringToBytes(String hex) {
          final byte[] addr;
          try {
              addr = Hex.decode(hex);
          } catch (DecoderException addressIsNotValid) {
              return null;
          }
  
          if (isValidAddress(addr))
              return addr;
          return null;
      }
docs: Decodes a hex string to address bytes and checks validity
  
  @param hex
  - a hex string of the address, e.g.,
  6c386a4b26f73c802f34673f7248bb118f97424a
  @return - decode and validated address byte[]