code: private Set<String> validateJobNetworkMode(final Job job) {
      final String networkMode = job.getNetworkMode();
  
      if (networkMode == null) {
        return emptySet();
      }
  
      final Set<String> errors = Sets.newHashSet();
  
      if (!VALID_NETWORK_MODES.contains(networkMode) && !networkMode.startsWith("container:")) {
        errors.add(String.format(
            "A Docker container's network mode must be %s, or container:<name|id>.",
            Joiner.on(", ").join(VALID_NETWORK_MODES)));
      }
  
      return errors;
    }
docs: Validate the Job's network mode.
  
  @param job The Job to check.
  
  @return A set of error Strings