Often nulls and exceptions are used when the code isn't finished, or in general sense to deal with unknowns. Neither is well fit for this.
I'd like instead to have "unknown" value/type which saves stack(or at least file/line) at time of its creation, but otherwise behaves like null/nothing. So that it can be easily ignored, but causes an exception when dereferencing is attempted. Having this additional creation-time stack information available in that exception should help debugging.