Omit properties from toJson() when value is null

[lukehutch]

Given a serializable class with nullable fields firstName and lastName:

@JsonSerializable()
class Person {
  final String? firstName, lastName;

  Person({required this.firstName, required this.lastName});

  factory Person.fromJson(Map<String, dynamic> json) => _$PersonFromJson(json);

  Map<String, dynamic> toJson() => _$PersonToJson(this);
}

currently the code generator generates the following toJson method given a nullable field someNullableField:

Map<String, dynamic> _$PersonToJson(Person instance) => <String, dynamic>{
      'firstName': instance.firstName,
      'lastName': instance.lastName,
    };

I don't know if null values are serialized into a JSON string as

{ "someNullableField": null }

of if the map entry is simply omitted by the JSON string serializer when the value is null, but either way, it would be more optimal in terms of time and space to only add non-null fields to the map:

Map<String, dynamic> _$PersonToJson(Person instance) => <String, dynamic>{
      if (instance.firstName != null) 'firstName': instance.firstName,
      if (instance.lastName != null) 'lastName': instance.lastName,
    };

Related:

• omit properties from toJson() when their value is an empty list #1369
• Default value for record fields #1340
• Generate null checking code if the property is nullable when using @JsonKey(fromJson) #1356

[jtmuller5]

Can't you just set includeIfNull to false?

[lukehutch]

I didn't know about that. Thank you!