code: public static byte[] defaultMachineId() {
          byte[] bestMacAddr = bestAvailableMac();
          if (bestMacAddr == null) {
              bestMacAddr = new byte[EUI64_MAC_ADDRESS_LENGTH];
              PlatformDependent.threadLocalRandom().nextBytes(bestMacAddr);
              logger.warn(
                      "Failed to find a usable hardware address from the network interfaces; using random bytes: {}",
                      formatAddress(bestMacAddr));
          }
          return bestMacAddr;
      }
docs: Returns the result of {@link #bestAvailableMac()} if non-{@code null} otherwise returns a random EUI-64 MAC
  address.