code: func (im *ImageManifest) assertValid() error {
  	if im.ACKind != ImageManifestKind {
  		return imKindError
  	}
  	if im.ACVersion.Empty() {
  		return errors.New(`acVersion must be set`)
  	}
  	if im.Name.Empty() {
  		return errors.New(`name must be set`)
  	}
  	return nil
  }
docs: // assertValid performs extra assertions on an ImageManifest to ensure that
  // fields are set appropriately, etc. It is used exclusively when marshalling
  // and unmarshalling an ImageManifest. Most field-specific validation is
  // performed through the individual types being marshalled; assertValid()
  // should only deal with higher-level validation.