createListProperty<T>  method 
    Null safety
Short hand helper function for initializing an EmpireListProperty.
See EmpireProperty for propertyName usages.
Example
late final EmpireListProperty planets;
planets = createListProperty(<String>['Mecury', 'Venus', 'Earth']);
Implementation
EmpireListProperty<T> createListProperty<T>(List<T> values,
    {String? propertyName}) {
  return EmpireListProperty(values, this, propertyName: propertyName);
}