ObjectTracker returns null

Vuforia SDK Version: 6.2.10 - Description with steps to reproduce: Hello everyone, I tried to get ObjectTracker from "TrackerManager.Instance" but it's null. As my experiment, TrackerManager.Instance isn't null but if you try to get some object from GetTracker whatever T class, it will return null. My code showing below https://gist.github.com/0x464D58/686f90f90f606535551b7819a55e06f3 I use Unity 5.6.1f1 64bit and Vuforia Unity SDK 6.2.10. I knew if this is bug issue, it takes a time to solve them but can I get ObjectTracker in a different way to load and active DataSet via coding? - Development OS (Mac OS X, Windows, Linux): Windows 10 (64bit) - Mobile OS and Version: Android 6.0 - Mobile Device Manufacturer and Model name: LG3 - Do the Vuforia Sample Applications show the same behavior?: Basically, it isn't contain what I want to do (DynamicDataSetLoader) in a sample.