fix($parse): default expressions of the form a.b to undefined

[lgalfaso]

When there is an expression of the form a.b and there is a recursion that specifies where the value should be placed, then when a == null then set the value of the returned identifier to undefined

Closes #11959

[lgalfaso]

@petebacondarwin can you take a look at this?

[petebacondarwin]

LGTM.

The commit message is a bit confusing though. It sounds to focused on the implementation rather than the issue that is being fixed.

How about:

fix($parse): set null reference properties to `undefined`

When there is an expression of the form `a.b` and where `a == null`, then set
the value of `a.b` to `undefined`.

Closes #11959

Or is that too general?

Other than that feel free to merge.

[petebacondarwin]

Well done on providing such a quick fix!

[lgalfaso]

Fixed and landed as d19504a