isNullTestable

class C {}
struct S1 {
    void opAssign(int*) {}
}
static assert(!isNullTestable!S1);
static assert( isNullTestable!C);
static assert( isNullTestable!(int*));

struct S2 {}
static assert(!isNullTestable!S2);
static assert(!isNullTestable!int);

class C2 {
    @disable this();
}
static assert(isNullTestable!C2);