not surport Dart SDK version: 3.1.0-89.0.dev (dev)

[htf6]

Because pub global activate depends on dart_mars from git which doesn't support null safety, version solving failed.

The lower bound of "sdk: '>=2.10.0 <3.0.0'" must be 2.12.0 or higher to enable null safety. For details, see https://dart.dev/null-safety