Custom constructors require all fields to be specified

[pauldemarco]

Custom constructors require all fields to be specified:

@data
class $Person {
  String name = 'Paul';

  @nullable
  double weight;

  int age;

  /// Generated code will complain that final field `weight` is not initialized
  $Person.genius()
  : name = 'Albert',
    age = 140;
}