coverage breaks with `@Tag` in v1.27.0

[felangel]

@Tags(['pull-request-only'])
library ensure_build_test;

import 'package:build_verify/build_verify.dart';
import 'package:test/test.dart';

void main() {
  test('ensure_build', () {
    expectBuildClean(packageRelativeDirectory: 'packages/bloc_tools');
  });
}

Test fails in v1.27.0 of pkg:test but passes in v1.26.3.
Removing @Tags(...) also makes the tests pass.

$ dart test --coverage=coverage && dart pub global run coverage:format_coverage --lcov --in=coverage --out=coverage/lcov.info --packages=.dart_tool/package_config.json --report-on=lib
00:00 +0: test/ensure_build_test.dart: (suite)                                                                                                                                                                                                                                                                                                                                                                                                                                                               
  Skip: Should only be run during pull request
00:00 +0 ~1: test/ensure_build_test.dart: (suite)                                                                                                                                                                                                                                                                                                                                                                                                                                                            type 'Null' is not a subtype of type 'List<Map<String, dynamic>>' in type cast
package:test_core/src/runner/coverage.dart 33:48  writeCoverage
package:test_core/src/runner/engine.dart 307:17   Engine.run.<fn>.<fn>
package:async/src/future_group.dart 79:15         FutureGroup.add.<fn>

This is an unexpected error. Please file an issue at http://github.com/dart-lang/test
with the stack trace and instructions for reproducing the error.
Unhandled exception:
type 'Null' is not a subtype of type 'List<Map<String, dynamic>>' in type cast
#0      writeCoverage (package:test_core/src/runner/coverage.dart:33:48)
<asynchronous suspension>
#1      Engine.run.<anonymous closure>.<anonymous closure> (package:test_core/src/runner/engine.dart:307:17)
<asynchronous suspension>
#2      FutureGroup.add.<anonymous closure> (package:async/src/future_group.dart:79:15)
<asynchronous suspension>

Link to CI failure: https://github.com/felangel/bloc/actions/runs/19545116043/job/55961821864?pr=4676

[natebosch]

looks related to #2517

[kevmoo]

Might be as easy as just handling the null case.

Wanna try a PR @felangel ?

[felangel]

Might be as easy as just handling the null case.

Wanna try a PR @felangel ?

Sure happy to 👍

[felangel]

@kevmoo done ✅
I didn't see any existing unit tests so let me know how you want to proceed, thanks!