@Override
  public final String getPropertyValue(final String propertyName) {
    for (GenericAttributeValue<String> value : getPropertyDefiningAttributes()) {
      if (propertyName.equals(value.getStringValue())) {
        return calcPropertyValue(propertyName);
      }
    }
    for (String implicitPropName : getImplicitPropertyNames()) {
      if (propertyName.equals(implicitPropName)) {
        return calcPropertyValue(propertyName);
      }
    }
    return null;
  }
@Override
  public final String getPropertyValue(final String propertyName)