toJson method
Implementation
@override
Map<String, dynamic> toJson() => <String, dynamic>{
'registration_month': registrationMonth,
'registration_year': registrationYear,
'phone_number_country_code': phoneNumberCountryCode,
'last_name_change_date': lastNameChangeDate,
'last_photo_change_date': lastPhotoChangeDate,
'@type': constructor,
};