[dart-dio] non-nullable model fields defined as nullable in generated dart

Using the example spec here the following snippet is generated

/// Outer
///
/// Properties:
/// * [results]
@BuiltValue()
abstract class Outer implements Built<Outer, OuterBuilder> {
  @BuiltValueField(wireName: r'results')
  BuiltList<int>? get results;
  Outer._();
  factory Outer([void updates(OuterBuilder b)]) = _$Outer;
  @BuiltValueHook(initializeBuilder: true)
  static void _defaults(OuterBuilder b) => b..results = ListBuilder();
  @BuiltValueSerializer(custom: true)
  static Serializer<Outer> get serializer => _$OuterSerializer();
}

When results is non-nullable I expect the type to be BuiltList<int> instead of BuiltList<int>?.

On this line you can see the template reads {{^isNullable}}{{^required}}?{{/required}}{{/isNullable}}, which seems backwards for the isNullable check.

Spec used to demonstrate issue is here
openapi-generator version: commit 031f0dcee692264681387bf8fbbece98f477801b (master as of now)

Start with modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class_members.mustache and compare its nullable and required conditionals with the reported output. Generate the Dart model from the linked example spec, then verify that the non-nullable results field is emitted as BuiltList rather than BuiltList?.