@Nonnull
  private List<ExtraDirectoryParameters> convertToExtraDirectoryParametersList(Object obj) {
    return project.files(obj).getFiles().stream()
        .map(file -> new ExtraDirectoryParameters(objects, project, file.toPath(), "/"))
        .collect(Collectors.toList());
  }
Helper method to convert {@code Object} to {@code List<ExtraDirectoryParameters>} in {@code
setFrom}.
jib-gradle-plugin/src/main/java/com/google/cloud/tools/jib/gradle/ExtraDirectoriesParameters.java