createNullProperty<T>  method 
    Null safety
- {String? propertyName}
 
Short hand helper function for initializing an EmpireProperty with a null value.
See EmpireProperty for propertyName usages.
Example
late final EmpireProperty<String?> name;
name = createNullProperty();
Implementation
EmpireProperty<T?> createNullProperty<T>({String? propertyName}) {
  return createProperty(null, propertyName: propertyName);
}