type 'Null' is not a subtype of type 'List<String>' in type cast

[jonasfj]

I didn't check if this is fixed in the master branch, but it appears for a few packages on pub.dev

$ export FLUTTER_ROOT=/workspace/flutter
$ ./reproduce-dartdoc-issue.sh input_country 2.1.0
Package dartdoc is currently active at version 6.2.0.
The package dartdoc is already activated at newest available version.
To recompile executables, first run `dart pub global deactivate dartdoc`.
Installed executable dartdoc.
Activated dartdoc 6.2.0.
Documenting input_country...                                                                                                                                                                                                           -
dartdoc 6.2.0 (/jonasfj/.pub-cache/global_packages/dartdoc/bin/dartdoc.dart-2.19.4.snapshot) failed: type 'Null' is not a subtype of type 'List<String>' in type cast
#0      _DartdocFileOption._valueAtFromFile (package:dartdoc/src/dartdoc_options.dart:967:47)
#1      _DartdocFileOption._valueAtFromFilesFirstFound (package:dartdoc/src/dartdoc_options.dart:892:15)
#2      _DartdocFileOption._valueAtFromFiles (package:dartdoc/src/dartdoc_options.dart:880:28)
#3      DartdocOptionArgFile.valueAt (package:dartdoc/src/dartdoc_options.dart:813:29)
#4      DartdocOptionContext.include (package:dartdoc/src/dartdoc_options.dart:1274:35)
#5      DartdocOptionContext.include (package:dartdoc/src/dartdoc_options.dart)
#6      PubPackageBuilder.getLibraries.<anonymous closure> (package:dartdoc/src/model/package_builder.dart:438:18)
#7      PubPackageBuilder._parseLibraries (package:dartdoc/src/model/package_builder.dart:252:30)
<asynchronous suspension>
#8      PubPackageBuilder.getLibraries (package:dartdoc/src/model/package_builder.dart:433:5)
<asynchronous suspension>
#9      PubPackageBuilder.buildPackageGraph (package:dartdoc/src/model/package_builder.dart:85:5)
<asynchronous suspension>
#10     Dartdoc.generateDocsBase (package:dartdoc/src/dartdoc.dart:202:24)
<asynchronous suspension>
#11     Dartdoc.generateDocs (package:dartdoc/src/dartdoc.dart:250:24)
<asynchronous suspension>
#12     Dartdoc.executeGuarded.<anonymous closure> (package:dartdoc/src/dartdoc.dart:288:9)
<asynchronous suspension>

Use the reproduce-dartdoc-issue.sh below to reproduce:

#!/bin/bash

set -e

DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"

P="$1"
V="$2"

if [ -z "$P" ]; then
  echo 'usage: ./reproduce-dartdoc-issue.sh <package> <version>'
  exit 1;
fi

if [ -z "$V" ]; then
  echo 'usage: ./reproduce-dartdoc-issue.sh <package> <version>'
  exit 1;
fi

cd $(mktemp -d)
curl -L "https://pub.dev/api/packages/$P/versions/$V/archive.tar.gz" | tar -xz
dart pub global activate dartdoc
dartdoc

[jcollins-g]

It is still present at head. It's due to a bad dartdoc_options.yaml, but we shouldn't crash just because of bad input here. Fix incoming in #3372.