def validate_icon(id)
      return nil unless JSS::DB_CNX.connected?
      raise JSS::NoSuchItemError, "No icon with id #{id}" unless JSS::Icon.all_ids.include? id
    end
def validate_icon(id)
      return nil unless JSS::DB_CNX.connected?
      raise JSS::NoSuchItemError, "No icon with id #{id}" unless JSS::Icon.all_ids.include? id
    end
Raise an error if an icon id is not valid