code: func (l *WorkItemLink) CheckValidForCreation() error {
  	if uuid.Equal(l.LinkTypeID, uuid.Nil) {
  		return errors.NewBadParameterError("link_type_id", l.LinkTypeID)
  	}
  	return nil
  }
docs: // CheckValidForCreation returns an error if the work item link
  // cannot be used for the creation of a new work item link.