unchecked_use_of_nullable_value for a checked nullable callback

[nex3]

When analyzing the following file with NNBD enabled:

int Function()? foo;

int callFoo() => foo != null ? foo() : 0;

I get the following error:

  error • An expression whose value can be 'null' must be null-checked before it can be dereferenced. • test.dart:3:32 • unchecked_use_of_nullable_value

This error seems bogus, since we are specifically are checking foo != null. Note that doing the check in an if statement also exhibits this error.

Tested with 2.12.0-110.0.dev.

[devoncarew]

Above, foo is a field; unfortunately, those don't type promote. There's a discussion of that here: #35525.

cc @leafpetersen @stereotype441 wrt improving the diagnostics we provide in these cases.

[srawlins]

Closing; working as specified.