code: func (m *kubeGenericRuntimeManager) GetImageRef(image kubecontainer.ImageSpec) (string, error) {
  	status, err := m.imageService.ImageStatus(&runtimeapi.ImageSpec{Image: image.Image})
  	if err != nil {
  		klog.Errorf("ImageStatus for image %q failed: %v", image, err)
  		return "", err
  	}
  	if status == nil {
  		return "", nil
  	}
  	return status.Id, nil
  }
docs: // GetImageRef gets the ID of the image which has already been in
  // the local storage. It returns ("", nil) if the image isn't in the local storage.