WpfDrawingDocument HitTest with rectangle always return null

Question

I'm using the following code to extract elements in a particular area:

var histTest = _drawingDocument.HitTest(new Rect(x, y, width, height), IntersectionDetail.Intersects);

Unfortunately, the hitTest elements are always null, and IsHit is false. Am I doing something wrong? Please guide me to fix this issue.

Regards, Jestin CI