void () { ak().foo(ak()); // test:cannot-convert:null? to AK! ak().foo(null); // test:cannot-convert:null? to AK! akn().foo(null); bk().foo(bk()); // test:cannot-convert:null? to B! bk().foo(null); ck().foo(ck()); // test:cannot-convert:null? to CK! ck().foo(null); // test:cannot-convert:null? to CK! ckn().foo(null); }