operator []= method
Sets a value by property name in backing.
Implementation
void operator []=(String? propertyName, dynamic value) {
final prop = properties[propertyName];
if (prop == null) {
throw ArgumentError("Invalid property access for '${entity.name}'. "
"Property '$propertyName' does not exist on '${entity.name}'.");
}
backing.setValueForProperty(prop, value);
}