Nullable.opEquals

bool opEquals(this This, Rhs)(auto ref Rhs rhs) if (!is(CommonType!(This, Rhs) == void))

If they are both null, then they are equal. If one is null and the other is not, then they are not equal. If they are both non-null, then they are equal if their values are equal.

bool opEquals(this  This,  Rhs)(auto  ref  Rhs rhs) if (is(CommonType!(This,  Rhs)  ==  void)  &&  is(typeof(this.get ==  rhs)))

Ditto