Attempt to read property "created_at" on null in – Laravel

The following are the function that I am trying to make work. I think I have the information required correct and the corresponding data also exist in the table but it is showing the error as above. Below are the function in my UserProfileController.

I’ve tried to change the column name from created_at to date_checkIn but it is showing the same error, both the columns exist in the database table as shown in my screenshots above. Please help

public function userClockOut(Request $r)
    {
        $result = [];
        $result['status'] = false;
        $result['message'] = "something error";

        $users = User::where('staff_id', $r->staff_id)->select(['staff_id', 'date_checkIn', 'time_checkOut', 'location_checkOut'])->first();

        $tt = AttendanceRecord::find($r->tt);
        $tt2 = AttendanceRecord::find($r->tt2);

        $tz = $tt->created_at;
        $tz2 = $tt2->updated_at;

        $date = Carbon::createFromFormat('Y-m-d', $tz, 'UTC');
        $time = Carbon::createFromFormat('H:i:s', $tz2, 'UTC');
        $date->setTimezone('Asia/Singapore');
        $time->setTimezone('Asia/Singapore');

        $users->date_checkIn = $date;
        $users->time_checkOut = $time;
        $users->location_checkOut = $r->location_checkOut;

        // Save the updated data to the database
        AttendanceRecord::updateOrCreate(
            ['staff_id' => $users->staff_id, 'date_checkIn' => $date],
            $users->toArray()
        );

        $result['data'] = $users;
        $result['status'] = true;
        $result['message'] = "suksess add data";

        return response()->json($result);
    }

Screenshots to show that the column exist in the database table :

https://paste.pics/f6103e8822c01f26bd23d500e0b0e9ad https://paste.pics/008df0256fd5ec20caff3772194cc0cf https://paste.pics/66cca657a49944e8087451c3b75967d3