code: func (gce *Cloud) findDiskByName(diskName string, zone string) (*gceDisk, error) {
  	disk, err := gce.service.Disks.Get(gce.projectID, zone, diskName).Do()
  	if err == nil {
  		d := &gceDisk{
  			Zone: lastComponent(disk.Zone),
  			Name: disk.Name,
  			Kind: disk.Kind,
  		}
  		return d, nil
  	}
  	if !isHTTPErrorCode(err, http.StatusNotFound) {
  		return nil, err
  	}
  	return nil, nil
  }
docs: // Returns a gceDisk for the disk, if it is found in the specified zone.
  // If not found, returns (nil, nil)