anchor.diff:    }
   
     Future<void>
  +      test_functionExpressionInvocation_extensionMember_allowsNull_explicit() async {
  +    await analyze('''
  +class C {}
  +extension E on C/*?*/ {
  +  void call() {}
  +}
  +f(C/*?*/ c) => E(c)();
  +''');
  +    var functoinExpressionInvocation =
  +        findNode.functionExpressionInvocation('E(c)()');
  +    visitSubexpression(functoinExpressionInvocation, 'void');
  +  }
  +
  +  Future<void>
         test_functionExpressionInvocation_extensionMember_disallowsNull() async {
       await analyze('''
   class C {}
  
positive.code:     var indexExpression = findNode.index('c[0]');
      visitSubexpression(indexExpression, 'int',
          changes: {indexExpression.target: isNullCheck});
    }
  
    Future<void> test_indexExpression_simple() async {
  
negative.code:     visitSubexpression(methodInvocation, 'void');
    }
  
    Future<void>
        test_methodInvocation_extensionMember_allowsNull_explicit() async {
      await analyze('''
  class C {}
  extension E on C/*?*/ {
    void foo() {}
  }
  f(C/*?*/ c) => E(c).foo();
  ''');
      var methodInvocation = findNode.methodInvocation('E(c).foo');
      visitSubexpression(methodInvocation, 'void');
    }
  
    Future<void> test_methodInvocation_extensionMember_disallowsNull() async {
      await analyze('''
  class C {}
  