`dart run` remote with empty version string fails

[sigurdm]

> dart run https://pub.dev/pana@
Resolving dependencies in `/tmp/HUIMZR/helperPackage/`... 
Error on line 5, column 18 of /tmp/HUIMZR/helperPackage/pubspec.yaml: Invalid version constraint: Cannot parse an empty string.
  ╷
5 │       "version": ""
  │                  ^^
  ╵

Perhaps we could special case the empty version constraint to be the null constraint (instead of the empty string)

[sigurdm]

cc @dcharkes

[dcharkes]

Would null basically get the last stable version? And effectively be the same as https://pub.dev/pana in pubspec terms?

[sigurdm]

Yes, null is a synonym for any. And that means the pub solver will try using the latest stable first.

[dcharkes]

Well if we want the json-esque command-line string to pubspec.yaml mapping, this should be an error, because it is not a null, it's an empty string. So, then it should be a usageException( in dartdev. WDYT? I think I'm fine with either solution.