how flutter map in for widget - flutter

Question

my json=
{
"result": {
"name": "json1",
"pages": [{
"zones": [{
"title": "title1"
},
{
"title": "title2"
}],
"id": 4
},
{
"zones": [{
"title": "title3"
},
{
"title": "title4"
}],
"id": 12
}],
"creatorUserName": "admin",
"id": 2
}
}
futurebuilder code
List post = snapshot.data["result"]["pages"];
return new Stack(
children: post.where((val) => val["id"] == 4).map((post) {
for (var item in post['zones']) {
print("title "+ item['title']);
Container(
child: Text(item["title"]),
); //Container
}
}).toList(),
); //Stack
Error code: Stack's children must not contain any null values, but a null value was found at index 0
enter image description here
help how can to build an algorithms
if get id = 4 zones -> Text(title1), Text(title2),
else id empty zones -> Text(title1), Text(title2), zones -> Text(title3), Text(title4),

Answer 1

Try
List post = snapshots.data["result"]["pages"];

Answer 2

First Make a model class for your JSON response using this amazing webpage, after that you can easily. call the needed data
import 'dart:convert';
YourModelClassName yourModelClassNameFromJson(String str) => YourModelClassName.fromJson(json.decode(str));
String yourModelClassNameToJson(YourModelClassName data) => json.encode(data.toJson());
class YourModelClassName {
Result result;
YourModelClassName({
this.result,
});
factory YourModelClassName.fromJson(Map<String, dynamic> json) => YourModelClassName(
result: Result.fromJson(json["result"]),
);
Map<String, dynamic> toJson() => {
"result": result.toJson(),
};
}
class Result {
String name;
List<Page> pages;
String creatorUserName;
int id;
Result({
this.name,
this.pages,
this.creatorUserName,
this.id,
});
factory Result.fromJson(Map<String, dynamic> json) => Result(
name: json["name"],
pages: List<Page>.from(json["pages"].map((x) => Page.fromJson(x))),
creatorUserName: json["creatorUserName"],
id: json["id"],
);
Map<String, dynamic> toJson() => {
"name": name,
"pages": List<dynamic>.from(pages.map((x) => x.toJson())),
"creatorUserName": creatorUserName,
"id": id,
};
}
class Page {
List<Zone> zones;
int id;
Page({
this.zones,
this.id,
});
factory Page.fromJson(Map<String, dynamic> json) => Page(
zones: List<Zone>.from(json["zones"].map((x) => Zone.fromJson(x))),
id: json["id"],
);
Map<String, dynamic> toJson() => {
"zones": List<dynamic>.from(zones.map((x) => x.toJson())),
"id": id,
};
}
class Zone {
String title;
Zone({
this.title,
});
factory Zone.fromJson(Map<String, dynamic> json) => Zone(
title: json["title"],
);
Map<String, dynamic> toJson() => {
"title": title,
};
}