QML_IMPORT_PATH error when adding a new qtquickcontrols2 file to the project

Steps to reproduce:

• Install Qt Design Studio 0.9 (on Windows)
• from File -> New File or Project -> Files and Classes ->  Qt Quick Controls -> Custom Switch

Expected result:

The Custom Switch is shown.

Actual result:

The Custom Switch does not open and a dialog saying about missing QML_IMPORT_PATH is opened. In Design Mode it shows that import Documents 1.0 QML module is not found. Checking the system's environment settings, there is no Qt set in the Path variables.