public Optional<AbsoluteUnixPath> getAppRoot() {
    if (appRoot == null) {
      return Optional.empty();
    }
    return Optional.of(AbsoluteUnixPath.fromPath(appRoot));
  }
Returns the user-specified app root in the container.

@return a user configured app root
jib-cli/src/main/java/com/google/cloud/tools/jib/cli/War.java