Failed assertion: line 13 pos 16: 'map['saleVal'] != is not true - firebase

Question

I'm trying to show my data in a simple bar chart from data stored on firestore.
The full error :
The following assertion was thrown building StreamBuilder<QuerySnapshot<Object?>>(dirty, state
_StreamBuilderBaseState<QuerySnapshot<Object?>, AsyncSnapshot<QuerySnapshot<Object?>>>#50e12):
'package:login_signup/Model/sales.dart': Failed assertion: line 13 pos 16: 'map['saleVal'] !=
is not true.
import 'package:cloud_firestore/cloud_firestore.dart';
class Sales{
final int saleVal ;
final String saleYear ;
final String colorVal ;
Sales(this.saleVal,this.colorVal,this.saleYear);
Sales.fromMap(Map<String, dynamic> map)
: assert(map['saleVal'] != null),
assert(map['saleYear'] != null),
assert(map['colorVal'] != null),
saleVal = map['saleVal'],
colorVal = map['colorVal'],
saleYear=map['saleYear'];
#override
String toString() => "Record<$saleVal:$saleYear:$colorVal>";
}
And this is the page for the chart where i have to show the sales via a chart bar
import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'Model/sales.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'rounded_button.dart';
class ChartScreen extends StatefulWidget {
#override
_ChartScreenState createState() => _ChartScreenState();
}
class _ChartScreenState extends State<ChartScreen> {
late List<charts.Series<Sales,String>> _seriesBarData;
late List<Sales> myData ;
_generateData(myData){
_seriesBarData = <charts.Series<Sales,String>>[];
_seriesBarData.add(
charts.Series(
domainFn : (Sales sales,_) => sales.saleYear.toString() ,
measureFn : (Sales sales,_) => sales.saleVal,
colorFn : (Sales sales,_) => charts.ColorUtil.fromDartColor(Color(int.parse(sales.colorVal))),
id:"Sales",
data: myData ,
labelAccessorFn: (Sales row,_) => "${row.saleYear}"
)
);
}
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.white,
body: _buildBody(context),
);
}
Widget _buildBody(BuildContext context){
return StreamBuilder<QuerySnapshot>(
stream: FirebaseFirestore.instance.collection('sales').snapshots(),
builder: (context,snapshot){
children: <Widget>[
RoundedButton(
colour: Colors.lightBlueAccent,
title: 'Dashboard',
onPressed: () {
Navigator.pushNamed(context, 'charts_screen');
},
),
];
if(!snapshot.hasData){
return LinearProgressIndicator();
}
else{
List<Sales> sales = snapshot.data!.docs
.map((snapshot) => Sales.fromMap(snapshot.data() as Map<String,dynamic>))
.toList();
return _buildChart(context, sales);
}
},
);
}
Widget _buildChart(BuildContext context , List<Sales> saledata){
List<Sales> myData ;
myData = saledata;
_generateData(myData){};
return Padding(
padding: EdgeInsets.all(8.0),
child: Container(
child: Center(
child:Column(
children: <Widget>[
Text ('Sales by Year',
style:TextStyle(fontSize:24.0 , fontWeight: FontWeight.bold),
),
SizedBox(height : 10.0, ),
/*Expanded(
child: charts.BarChart(_seriesBarData,
animate : true,
animationDuration: Duration(seconds:5),
behaviors : [
new charts.DatumLegend(
entryTextStyle : charts.TextStyleSpec(color: charts.MaterialPalette.purple.shadeDefault,
fontFamily: 'Google',
fontSize:18),
)
],
),
),*/
],
),
),
),
);
}
}

Answer 1

Your error occures on Sales.fromMap on the assert(map['saleVal'] != null) line. So, your map['saleVal'] happens to be null. Maybe you should drop assert lines and just use null check with default values in case of null value. Like:
Sales.fromMap(Map<String, dynamic> map)
: saleVal = map['saleVal'] ?? 0, // default value in case of null
colorVal = map['colorVal'] ?? '',
saleYear = map['saleYear'] ?? '';
Or maybe make your properties nullable, like:
final int? saleVal;
final String? saleYear;
final String? colorVal;