Make the uri property of RedirectException nullable

[brianquinlan]

Change

Change:

class RedirectException implements HttpException {
-  Uri get uri => ...
+  Uri? get uri => ...
}

Rationale

This will allow us to cleanly fix #49012, which causes a StateError when there is no available uri.

Impact

This will only break code that uses the RedirectException class directly and does not handle the null uri case.

Code that works with the HttpException base class will not need to be changed because uri is already nullable in that class.

This change does not break any Google code or any third-party code used by Google.

Mitigation

Users must handle a possible null return from RedirectException.uri.

[a-siva]

//cc @lrhn

[itsjustkevin]

@vsmenon @Hixie @grouma Could you all take a look at this breaking change proposal?

[grouma]

I didn't find any usages of RedirectException.uri inside Google3. I assume this doesn't impact HttpException which has the non nullable requestUrl member. This is referenced in a handful of places.

[brianquinlan]

@grouma If you are referring to the HttpException in ...xbid/ui/common/exceptions/lib/exceptions.dart then that class is in a completely different class hierarchy.

[Hixie]

I have no opinion on this change.

[brianquinlan]

@vsmenon It's all up to you ;-)

[vsmenon]

lgtm

[brianquinlan]

Fixed in e5af733