Hit a snag

[FeepingCreature]

I've hit a bit of a snag while implementing the PR.

https://issues.dlang.org/show_bug.cgi?id=18775 seems to make 
deprecating the implicit conversion basically impossible, because 
the deprecation will be triggered on every UFCS access to a 
Nullable, no matter whether it actually uses .get or not. DMD 
seems to generally have issues isolating failed struct lookups 
properly.