downgrade --tighten fails with a workspace

[kevmoo]

Environment

Dart SDK version: 3.6.0-129.0.dev (dev) (Thu Aug 8 05:02:43 2024 -0700) on "macos_arm64"

Problem

• sync https://github.com/google/googleapis.dart/ at google/googleapis.dart@d6e5541
• run dart pub downgrade --tighten

Expected behavior

• it works!

Actual behavior

Changed 78 dependencies!
75 packages have newer versions incompatible with dependency constraints.
Try `dart pub outdated` for more information.
Null check operator used on a null value
package:pub/src/entrypoint.dart 1405:49                         Entrypoint.tighten
package:pub/src/command/downgrade.dart 100:34                   DowngradeCommand.runProtected
===== asynchronous gap ===========================
package:pub/src/command.dart 196:7                              PubCommand.run
===== asynchronous gap ===========================
package:args/command_runner.dart 212:13                         CommandRunner.runCommand
===== asynchronous gap ===========================
package:dartdev/dartdev.dart 236:18                             DartdevRunner.runCommand
===== asynchronous gap ===========================
package:dartdev/dartdev.dart 47:16                              runDartdev
===== asynchronous gap ===========================
/Volumes/Work/s/w/ir/x/w/sdk/pkg/dartdev/bin/dartdev.dart 13:5  main
This is an unexpected error. The full log and other details are collected in:

    /Users/kevmoo/.pub-cache/log/pub_log.txt

Consider creating an issue on https://github.com/dart-lang/pub/issues/new
and attaching the relevant parts of that log file.