NoSuchMethodError: The method 'map' was called on null - json

Question

[ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The method 'map' was called on null.
E/flutter (19718): Receiver: null
E/flutter (19718): Tried calling: map(Closure: (dynamic) => SeriesNo)
I tried json_annotation and json Serieizable but don't work.According my model one.json is ok.but two.json is reques error happen as title.How to solve.I known series no is error but i have no idea how to solve.
This is one.json
{
"bookDetail": {
"title": "aaa",
"author": "aaa",
"image": "https://",
"text": "aaa",
"series_no": [
{
"id": 2
}
],
"created_at": "2019-08-27 15:19:10"
}
}
This is two.json
{
"bookDetail": {
"title": "Test",
"author": "TEst",
"image": "https:/riv19q9x.png",
"text": "Test",
"series_no": null,
"created_at": "2019-08-27 15:13:56"
}
}
This is detail.model using bloc flutter
class BookDetailModel {
BookDetail bookDetail;
BookDetailModel({
this.bookDetail,
});
factory BookDetailModel.fromJson(Map<String, dynamic> json) =>
new BookDetailModel(
bookDetail: BookDetail.fromJson(json["bookDetail"]),
);
Map<String, dynamic> toJson() => {
"bookDetail": bookDetail.toJson(),
};
}
#JsonSerializable(nullable: true)
class BookDetail {
String title;
String author;
String image;
String text;
List<SeriesNo> seriesNo;
DateTime createdAt;
BookDetail({
this.title,
this.author,
this.image,
this.text,
this.seriesNo,
this.createdAt,
});
factory BookDetail.fromJson(Map<String, dynamic> json) => new BookDetail(
title: json["title"],
author: json["author"],
image: json["image"],
text: json["text"],
seriesNo: new List<SeriesNo>.from(
json["series_no"].map((x) => SeriesNo.fromJson(x))),
createdAt: DateTime.parse(json["created_at"]),
);
Map<String, dynamic> toJson() => {
"title": title,
"author": author,
"image": image,
"text": text,
"series_no": new List<dynamic>.from(seriesNo.map((x) => x.toJson())),
"created_at": createdAt.toIso8601String(),
};
}
#JsonSerializable(nullable: true)
class SeriesNo {
int id;
SeriesNo({
this.id,
});
factory SeriesNo.fromJson(Map<String, dynamic> json) => new SeriesNo(
id: json["id"],
);
Map<String, dynamic> toJson() => {
"id": id,
};
}

Answer 1

Try to verify if is not null before:
seriesNo: json["series_no"] != null ? new List<SeriesNo>.from( json["series_no"].map((x) => SeriesNo.fromJson(x))) : List<SeriesNo>().
This is answer for my question.Crd #Stel

Answer 2

try placing seriesNo as dynamic and placing the remaining fields
class BookDetailModel {
BookDetail bookDetail;
BookDetailModel({
this.bookDetail,
});
factory BookDetailModel.fromJson(Map<String, dynamic> json) => BookDetailModel(
bookDetail: BookDetail.fromJson(json["bookDetail"]),
);
Map<String, dynamic> toJson() => {
"bookDetail": bookDetail.toJson(),
};
}
class BookDetail {
String title;
String author;
String image;
String text;
dynamic seriesNo;
DateTime createdAt;
BookDetail({
this.title,
this.author,
this.image,
this.text,
this.seriesNo,
this.createdAt,
});
factory BookDetail.fromJson(Map<String, dynamic> json) => BookDetail(
title: json["title"],
author: json["author"],
image: json["image"],
text: json["text"],
seriesNo: json["series_no"],
createdAt: DateTime.parse(json["created_at"]),
);
Map<String, dynamic> toJson() => {
"title": title,
"author": author,
"image": image,
"text": text,
"series_no": seriesNo,
"created_at": createdAt.toIso8601String(),
};
}

Answer 3

If it's a List and a double value, how can it be written even if it's correct? I got this problem. Please see my link.Link Linkclass
Food _$FoodFromJson(Map<String, dynamic> json) => Food(
ingredient: (json['ingredient'] as List<dynamic>)
.map((e) => e as String)
.toList(),
quantity:
(json['quantity'] as List<dynamic>).map((e) => e as String).toList(),
uom: (json['uom'] as List<dynamic>).map((e) => e as String).toList(),
step: (json['step'] as List<dynamic>).map((e) => e as String).toList(),
);