@Nested
  @Nullable
  public JibExtension getJib() {
    return jibExtension;
  }
This will call the property {@code "jib"} so that it is the same name as the extension. This
way, the user would see error messages for missing configuration with the prefix {@code jib.}.

@return the {@link JibExtension}.
jib-gradle-plugin/src/main/java/com/google/cloud/tools/jib/gradle/BuildImageTask.java