Why does nobody seem to think that `null` is a serious problem in D?

[Tony]

On Saturday, 1 December 2018 at 11:16:49 UTC, Dukc wrote:
> This is great when it works, but the problem is that it would 
> be gargantuan effort -and compile time sink- to make it work 
> perfectly. When it's just about if-else if chains, switches or 
> boolean logic as in the example, the analysis won't be too 
> complicated. But swap those booleans out for a string, and make 
> the conditions to test whether it's a phone number, and whether 
> it satisfies some predicate implemented in a foreign language, 
> and you'll see where the problem is.

I think he is just talking about the compiler or static analyzer 
seeing if a variable has been given a value before it is used, 
not if it was given a valid value.