field selection with ? on null now produces an error

[mtaufen]

Describe the bug
I think this change happened in #922.

For example, given yaml like:

foo:
  bar: null

and CEL like:

foo.?bar.?baz.orValue("not there")

behavior changes from returning "not there" to throwing a no such key error.

To Reproduce
Check which components this affects:

• parser
• checker
• interpreter

Expected behavior
Expected "not there" to be returned.

Additional context

I tried reverting the change from #922 and it makes things work the way I expect.

[TristonianJones]

Thanks for the report. I'll give it a look.