anchor.diff:  
     test_binary_nullType() async {
       await assertNoErrorsInCode(r'''
  -@pragma('analyzer:non-nullable')
  -library foo;
  -
   m() {
     Null x;
     x ?? 1;
  
positive.code: 
    test_deadBlock_if_debugConst_prefixedIdentifier2() async {
      newFile('/test/lib/lib2.dart', content: r'''
  library lib2;
  class A {
    static const bool DEBUG = false;
  }''');
      await assertNoErrorsInCode(r'''
  library L;
  import 'lib2.dart';
  f() {
    if(A.DEBUG) {}
  
negative.code: 
    test_deadBlock_if_debugConst_propertyAccessor() async {
      newFile('/test/lib/lib2.dart', content: r'''
  class A {
    static const bool DEBUG = false;
  }''');
      await assertNoErrorsInCode(r'''
  import 'lib2.dart' as LIB;
  f() {
    if(LIB.A.DEBUG) {}
  