code: func (mc MongoClient) UpdateRegistration(reg contract.Registration) error {
  	var mapped models.Registration
  	id, err := mapped.FromContract(reg)
  	if err != nil {
  		return err
  	}
  
  	mapped.TimestampForUpdate()
  
  	return mc.updateId(db.ExportCollection, id, mapped)
  }
docs: // Update a registration
  // UnexpectedError - problem updating in database
  // NotFound - no registration with the ID was found