TaskScheduler RegisterTaskDefinition fails with NULL path in Win10 - c++

Question

According to this MSDN doc, we may pass NULL for the path argument:
path [in]
The name of the task. If this value is NULL, the task will be registered in the root task folder and the task name will be a GUID value created by the Task Scheduler service.
I have a code that use this behavior. The code works fine in Win7 and 8.1, but not in my Win10 box (ver 1709 64-bit, build 16299). In Win10, it will return 0x80070005 aka "Access Denied" when path is NULL. If I specify a name like "Foobar", it will work fine.
Test code:
// Link comsuppw.lib and taskschd.lib.
#include <stdio.h>
#include <windows.h>
#include <atlbase.h>
#include <atlstr.h>
#include <shlobj.h>
#include <taskschd.h>
#include <comutil.h>
class AutoHR {
HRESULT hr;
public:
void operator=(HRESULT hr)
{
this->hr = hr;
if (FAILED(hr)) {throw *this;}
}
HRESULT GetHR() const { return hr; }
};
static void TestTaskSched()
{
AutoHR hr;
CComPtr<ITaskService> taskSvc;
CComPtr<ITaskFolder> taskFol;
CComPtr<ITaskDefinition> taskDef;
CComPtr<IActionCollection> taskAC;
CComPtr<IAction> taskAction;
CComPtr<IExecAction> taskEA;
CComPtr<IRegisteredTask> registeredTask;
try {
hr = taskSvc.CoCreateInstance(CLSID_TaskScheduler, nullptr, CLSCTX_ALL);
hr = taskSvc->Connect(CComVariant(),CComVariant(),CComVariant(),CComVariant());
hr = taskSvc->GetFolder(_bstr_t(L""), &taskFol);
hr = taskSvc->NewTask(0, &taskDef);
hr = taskDef->get_Actions(&taskAC);
hr = taskAC->Create(TASK_ACTION_EXEC, &taskAction);
hr = taskAction.QueryInterface<IExecAction>(&taskEA);
hr = taskEA->put_Path(_bstr_t(L"C:\\Windows\\System32\\cmd.exe"));
hr = taskEA->put_Arguments(_bstr_t(L"/k echo Testing"));
// Note that NULL is passed as the first argument.
hr = taskFol->RegisterTaskDefinition(nullptr, taskDef,
TASK_CREATE_OR_UPDATE, CComVariant(), CComVariant(),
TASK_LOGON_NONE, CComVariant(), &registeredTask);
MessageBoxW(nullptr, L"Succeeded!", L"OK", MB_ICONINFORMATION);
}
catch (AutoHR const &autohr) {
WCHAR buf[99] = {0};
wsprintfW(buf, L"HRESULT error 0x%.8X\n", autohr.GetHR());
MessageBoxW(nullptr, buf, nullptr, MB_ICONERROR);
}
}
int main()
{
HRESULT hr = CoInitializeEx(nullptr, COINIT_APARTMENTTHREADED);
if (SUCCEEDED(hr))
{
TestTaskSched();
CoUninitialize();
}
return 0;
}
Test result:
Questions:
1) Is there a behavior change between Win10 and older Windows? I suspect there is, but I cannot find any doc that mentions it.
2) Any good alternative for this behavior? I hope I don't have to generate GUID by myself for temporary task creation.