code: func (mc MongoClient) UpdateValueDescriptor(cvd contract.ValueDescriptor) error {
  	// See if the name is unique if it changed
  	chk, err := mc.getValueDescriptor(bson.M{"name": cvd.Name})
  	if err != db.ErrNotFound {
  		if err != nil {
  			return err
  		}
  
  		// IDs are different -> name not unique
  		if chk.Id.Hex() != cvd.Id && cvd.Id != chk.Uuid {
  			return db.ErrNotUnique
  		}
  	}
  
  	var mapped models.ValueDescriptor
  	id, err := mapped.FromContract(cvd)
  	if err != nil {
  		return err
  	}
  
  	mapped.Modified = db.MakeTimestamp()
  
  	return mc.updateId(db.ValueDescriptorCollection, id, mapped)
  }
docs: // Update a value descriptor
  // First use the ID for identification, then the name
  // TODO: Check for the valid printf formatting
  // 404 not found if the value descriptor cannot be found by the identifiers