code: func (mc MongoClient) ValueDescriptorById(id string) (contract.ValueDescriptor, error) {
  	query, err := idToBsonM(id)
  	if err != nil {
  		return contract.ValueDescriptor{}, err
  	}
  
  	mvd, err := mc.getValueDescriptor(query)
  	if err != nil {
  		return contract.ValueDescriptor{}, err
  	}
  	return mvd.ToContract(), nil
  }
docs: // Return a value descriptor based on the id
  // Return NotFoundError if there is no value descriptor for the id