// address. Here's a sample:
  //
  //      input: "1111:2222:3333::7777:8888"
  //     before: { 11, 11, 22, 22, 33, 33, 00, 00, 77, 77, 88, 88, 00, 00, 00, 00  }
  //   compress: 6
  //          b: 10
  //      after: { 11, 11, 22, 22, 33, 33, 00, 00, 00, 00, 00, 00, 77, 77, 88, 88 }
  //
  if (b != address.size) {
    if (compress == -1) return null // Address didn't have compression or enough groups.