code: func (m *Manager) GetAvatarFile(hash string) ([]byte, error) {
  	var file struct {
  		Hash string
  		File []byte
  	}
  
  	err := m.getAvatarFileCollection().Find(bson.M{"hash": hash}).One(&file)
  	if err == mgo.ErrNotFound {
  		return nil, nil
  	}
  	return file.File, err
  }
docs: // GetAvatarFile gets the avatar file associated with a hash