@Input
  @Nullable
  @Optional
  public String getImage() {
    if (System.getProperty(PropertyNames.TO_IMAGE) != null) {
      return System.getProperty(PropertyNames.TO_IMAGE);
    }
    return image.getOrNull();
  }
Object in {@link JibExtension} that configures the target image.
jib-gradle-plugin/src/main/java/com/google/cloud/tools/jib/gradle/TargetImageParameters.java