std.variant Is Everything Cool About D

[helxi]

On Thursday, 29 March 2018 at 14:10:39 UTC, Mike Parker wrote:
> Jared Hanson (a.k.a Meta and MetaLang around these parts) was 
> inspired by an article titled "std::visit is everything wrong 
> with modern C++" to contrast it with D's std.variant.visit. The 
> result is this well-written post for the D Blog.
>
> The blog:
> https://dlang.org/blog/2018/03/29/std-variant-is-everything-cool-about-d/
>
> Reddit:
> https://www.reddit.com/r/programming/comments/881hmi/stdvariant_is_everything_cool_about_d/

What is the difference between 
https://dlang.org/phobos/std_typecons.html#Nullable and 
Algebraic!(T, typeof(null))?