factory fromJson and static fromJson provide two different g.dart result

[RubyRook]

I want to make code much shorter without use JsonConverter. While factory fromJson cannot return null I need to use static fromJson instead. But, g.dart file didn't provide what i want.

Example with factory:
`import 'package:json_annotation/json_annotation.dart';

part 'di.category.g.dart';

@JsonSerializable(explicitToJson: true,)
class DiCategory {
String id;
String en_name;
String km_name;
String slug;
String parent;
bool popular;
DiIcon? icon;

DiCategory({
required this.id,
required this.en_name,
required this.km_name,
required this.slug,
required this.parent,
required this.popular,
this.icon,
});

factory DiCategory.fromJson(Map<String, dynamic> json) => _$DiCategoryFromJson(json);
Map<String, dynamic> toJson()=> _$DiCategoryToJson(this);
}

@JsonSerializable()
class DiIcon {
String url;
String width;
String height;

DiIcon({
required this.url,
required this.width,
required this.height,
});

factory DiIcon.fromJson(Object? json) => _$DiIconFromJson(json is Map<String, dynamic> ? json:{});
Map<String, dynamic> toJson()=> _$DiIconToJson(this);
}`

Inside di.category.g.dart
DiCategory _$DiCategoryFromJson(Map<String, dynamic> json) => DiCategory( id: json['id'] as String, en_name: json['en_name'] as String, km_name: json['km_name'] as String, slug: json['slug'] as String, parent: json['parent'] as String, popular: json['popular'] as bool, icon: json['icon'] == null ? null : DiIcon.fromJson(json['icon']), );

Example with static:
`import 'package:json_annotation/json_annotation.dart';

part 'di.category.g.dart';

@JsonSerializable(explicitToJson: true,)
class DiCategory {
String id;
String en_name;
String km_name;
String slug;
String parent;
bool popular;
DiIcon? icon;

DiCategory({
required this.id,
required this.en_name,
required this.km_name,
required this.slug,
required this.parent,
required this.popular,
this.icon,
});

factory DiCategory.fromJson(Map<String, dynamic> json) => _$DiCategoryFromJson(json);
Map<String, dynamic> toJson()=> _$DiCategoryToJson(this);
}

@JsonSerializable()
class DiIcon {
String url;
String width;
String height;

DiIcon({
required this.url,
required this.width,
required this.height,
});

static DiIcon? fromJson(Object? json) => json is Map<String, dynamic> ? _$DiIconFromJson(json):null;
Map<String, dynamic> toJson()=> _$DiIconToJson(this);
}
`
Inside di.category.g.dart

DiCategory _$DiCategoryFromJson(Map<String, dynamic> json) => DiCategory( id: json['id'] as String, en_name: json['en_name'] as String, km_name: json['km_name'] as String, slug: json['slug'] as String, parent: json['parent'] as String, popular: json['popular'] as bool, icon: json['icon'] == null ? null : DiIcon.fromJson(json['icon'] as Map<String, dynamic>), );

• The difference is that, why static fromJson generate with DiIcon.fromJson(json['icon'] as Map<String, dynamic>) and factory fromJson generate with DiIcon.fromJson(json['icon']) while both static and factory fromJson have same parameter data type Object? json
• The problem is that, it no error when i use with factory if json['icon'] not Map<String, dynamic> but it will when i use with static because DiIcon.fromJson(json['icon'] as Map<String, dynamic>)
• One more thing, it save me a lot of time if compare with implements JsonConverter while my purpose just check json data type and return null is invalid.