code: func (d *DotGit) Shallow() (billy.File, error) {
  	f, err := d.fs.Open(shallowPath)
  	if err != nil {
  		if os.IsNotExist(err) {
  			return nil, nil
  		}
  
  		return nil, err
  	}
  
  	return f, nil
  }
docs: // Shallow returns a file pointer for read to the shallow file