default null syntax

[He-Pin]

Motivation: when ?. is means we can call select on a nullable value, but it still throws Field does not exists exception.

What about using a obj.b? or obj['b'?] syntax to express: if bdoes not exists inobj, then returnnull` instead of an error.

• obj.b?
• obj["b"?]

or, we can just use std.get method