Snapshot.data not showing data occasionally - flutter

Question

I have a FutureBuilder widget and when Flutter communicates with Firebase, it doesn't show the data. But, whenever I remove two fields I recently added out of the 6, it works and show the data. The fields to be removed are incomeTotal and expenseTotal
Code
Read data function
Stream<List<CardDetails>> readCards() => FirebaseFirestore.instance
.collection('cards')
.snapshots()
.map((snapshot) => snapshot.docs
.map((doc) => CardDetails.fromJson(doc.data()))
.toList());
Load data onto widget
StreamBuilder<List<CardDetails>>(
stream: readCards(),
builder: (context, snapshot) {
if (!snapshot.hasData) {
return const Center(
child: CircularProgressIndicator());
} else if (snapshot.hasError) {
return const Text("error");
} else if (snapshot.hasData &&
snapshot.data!.isEmpty) {
return Container(
margin: const EdgeInsets.all(10),
width: double.infinity,
decoration: BoxDecoration(
color:
const Color.fromARGB(50, 0, 0, 0),
borderRadius:
BorderRadius.circular(20)),
child: Transform.scale(
scale: 1.5,
child: Lottie.asset(
"lib/images/space_animation.json")),
);
} else {
final cards = snapshot.data!;
if (cardIdOfficial == '') {
WidgetsBinding.instance
.addPostFrameCallback((_) {
setState(() {
cardIdOfficial = snapshot
.data![_pageViewController
.initialPage]
.id;
});
});
}
return PageView(
padEnds: false,
controller: _pageViewController,
onPageChanged: (value) => {
setState(() {
cardIdOfficial =
snapshot.data![value].id;
})
},
physics: const ClampingScrollPhysics(),
children:
cards.map(buildCards).toList());
}
}),
Model
class CardDetails {
final String id;
final String title;
final double balance;
final int cardDigits;
final int incomeTotal;
final int expenseTotal;
CardDetails({
required this.id,
required this.title,
required this.balance,
required this.cardDigits,
required this.incomeTotal,
required this.expenseTotal,
});
Map<String, dynamic> toJson() => {
'id': id,
'title': title,
'balance': balance,
'cardDigits': cardDigits,
'incomeTotal': incomeTotal,
'expenseTotal': expenseTotal,
};
static CardDetails fromJson(Map<String, dynamic> json) => CardDetails(
id: json['id'],
title: json['title'],
balance: json['balance'],
cardDigits: json['cardDigits'],
incomeTotal: json['incomeTotal'],
expenseTotal: json['expenseTotal']);
}
Everything was fine until I added those two fields, when I remove them everything looks fine. What I also did was change the variable name to just income instead of incomeTotal and ran it again, it worked but then this happened again twice.
Flutter doctor
[✓] Flutter (Channel stable, 3.7.3, on macOS 11.6.3 20G415 darwin-arm64, locale en-US)
[!] Android toolchain - develop for Android devices (Android SDK version 33.0.0)
✗ cmdline-tools component is missing
Run `path/to/sdkmanager --install "cmdline-tools;latest"`
See https://developer.android.com/studio/command-line for more details.
✗ Android license status unknown.
Run `flutter doctor --android-licenses` to accept the SDK licenses.
See https://flutter.dev/docs/get-started/install/macos#android-setup for more details.
[✓] Xcode - develop for iOS and macOS (Xcode 13.2.1)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2021.2)
[✓] IntelliJ IDEA Community Edition (version 2022.1.3)
[✓] VS Code (version 1.74.2)
[✓] VS Code (version 1.64.2)
[✓] Connected device (3 available)
[✓] HTTP Host Availability
Flutter dependencies
dependencies:
- cloud_firestore 4.3.1 [cloud_firestore_platform_interface cloud_firestore_web collection firebase_core firebase_core_platform_interface flutter meta]
- cupertino_icons 1.0.5
- custom_refresh_indicator 2.0.1 [flutter]
- firebase_core 2.4.1 [firebase_core_platform_interface firebase_core_web flutter meta]
- fluentui_icons 1.0.0 [flutter]
- fluentui_system_icons 1.1.190 [flutter]
- flutter 0.0.0 [characters collection js material_color_utilities meta vector_math sky_engine]
- flutter_slidable 2.0.0 [flutter]
- gap 2.0.1 [flutter]
- google_fonts 3.0.1 [flutter http path_provider crypto]
- google_nav_bar 5.0.6 [flutter]
- grouped_list 5.1.2 [flutter]
- intl 0.18.0 [clock meta path]
- lottie 2.2.0 [archive flutter path vector_math]
- metaballs 1.4.2 [flutter]
- provider 6.0.5 [collection flutter nested]
- sizer 2.0.15 [universal_io flutter]
- smooth_page_indicator 1.0.0+2 [flutter]
What happens
(https://i.stack.imgur.com/Wmaks.png)
What happens when I remove the two fields, what needs to happen (https://i.stack.imgur.com/YcPCY.png)

Answer 1

Your code looks fine, as far as I can tell. One possible issue I can think of:
Are you sure that every document within the cards collection in your Firestore database has those fields present and are integer values?
If one of those values wasn’t present on a document (or was of the wrong type), your deserialization (fromJson) would blow up.
In the past I’ve had trouble with this because it’s not always obvious that an error is being thrown - it’s sometimes swallowed within the internals of the stream.