@Override
  public List<? extends ExtraDirectoriesConfiguration> getExtraDirectories() {
    for (ExtraDirectoryParameters path : jibExtension.getExtraDirectories().getPaths()) {
      if (path.getFrom().equals(Paths.get(""))) {
        throw new IllegalArgumentException(
            "Incomplete extraDirectories.paths configuration; source directory must be set");
      }
    }
    return jibExtension.getExtraDirectories().getPaths();
  }
Gradle-specific adapter for providing raw configuration parameter values.
jib-gradle-plugin/src/main/java/com/google/cloud/tools/jib/gradle/GradleRawConfiguration.java