difference between x = Nullable.init and x.nullify

[Kagamin via Digitalmars-d-learn]

On Saturday, 3 June 2017 at 06:19:29 UTC, Jonathan M Davis wrote:
> Assigning Nullable!Test.init is equivalent to setting the 
> internal value to Test.init and setting _isNull to false.

Eh? Does it mean Nullable is default initialized to some non-null 
default value?