Nullability bug in `_network_image.io.dart`

[egaga]

Steps to Reproduce

The following code fails before throwing exception!

if (response.statusCode != HttpStatus.ok) {
// The network may be only temporarily unavailable, or the file will be
// added on the server later. Avoid having future calls to resolve
// fail to check the network again.
await response.drain<List<int>>();
throw image_provider.NetworkImageLoadException(statusCode: response.statusCode, uri: resolved);
}

Expected results:

This should be invoked:
throw image_provider.NetworkImageLoadException(statusCode: response.statusCode, uri: resolved);

Actual results:

I/flutter (18983): The following _CastError was thrown resolving an image codec:
I/flutter (18983): type 'Null' is not a subtype of type 'List<int>' in type cast
I/flutter (18983): 
I/flutter (18983): When the exception was thrown, this was the stack:
I/flutter (18983): #1      NetworkImage._loadAsync (package:flutter/src/painting/_network_image_io.dart:99:24)
I/flutter (18983): <asynchronous suspension>

Logs

[✓] Flutter (Channel stable, 2.2.3, on macOS 11.5.2 20G95 darwin-x64, locale en-FI)
    • Flutter version 2.2.3 at /Users/egaga/dev/flutter
    • Framework revision f4abaa0735 (8 weeks ago), 2021-07-01 12:46:11 -0700
    • Engine revision 241c87ad80
    • Dart version 2.13.4

[TahaTesser]

Hi @egaga

I/flutter (18983): The following _CastError was thrown resolving an image codec:
I/flutter (18983): type 'Null' is not a subtype of type 'List' in type cast

Can you please provide a reproducible sample for this?

[egaga]

Not yet, not sure if have time to minimize, but I can give you a little bit context:

Image.network has https url to Amazon S3 bucket.
Then the image is removed from the Amazon and when the Flutter app screen gets rebuild/re-rendered this happens.

I know it would be important to provide an example, and I am sorry that I haven't.

[egaga]

Here is a working example, requires the template produced by flutter create bug.

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Image Network error bug',
      home: _ImageNetworkBuggy(),
    );
  }
}

class _ImageNetworkBuggy extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Image.network("https://upload.wikimedia.org/wikipedia/commons/c/c4/DNA_double_helix_horizontal2.png")
      ),
    );
  }
}

The point is that the image url does not exist.

[TahaTesser]

@egaga
Both latest stable and master don't throw mull safety error using your code sample

[        ] For a more detailed help message, press "h". To quit, press "q".
[   +1 ms] An Observatory debugger and profiler on Chrome is available at: http://127.0.0.1:49342/uKos-S7cet8=
[ +463 ms] DevTools activation throttled until 2021-09-18 00:20:49.454218.
[ +583 ms] The Flutter DevTools debugger and profiler on Chrome is available at:
                    http://127.0.0.1:9101?uri=http://127.0.0.1:49342/uKos-S7cet8=
[  +38 ms] ══╡ EXCEPTION CAUGHT BY IMAGE RESOURCE SERVICE ╞════════════════════════════════════════════════════
[   +2 ms] The following ImageCodecException was thrown resolving an image codec:
[   +1 ms] Failed to load network image.
[   +2 ms] Image URL: https://upload.wikimedia.org/wikipedia/commons/c/c4/DNA_double_helix_horizontal2.png
[   +1 ms] Server response code: 404
[   +2 ms] When the exception was thrown, this was the stack
[   +1 ms] Image provider:
[   +1 ms]   NetworkImage("https://upload.wikimedia.org/wikipedia/commons/c/c4/DNA_double_helix_horizontal2.png",
[        ]   scale: 1)
[        ] Image key:
[        ]   NetworkImage("https://upload.wikimedia.org/wikipedia/commons/c/c4/DNA_double_helix_horizontal2.png",
[        ]   scale: 1)
[        ] ════════════════════════════════════════════════════════════════════════════════════════════════════