code: func (b Build) MarshalJSON() ([]byte, error) {
  	var ccBuild struct {
  		Package struct {
  			GUID string `json:"guid"`
  		} `json:"package"`
  	}
  
  	ccBuild.Package.GUID = b.PackageGUID
  
  	return json.Marshal(ccBuild)
  }
docs: // MarshalJSON converts a Build into a Cloud Controller Application.