Adding a SimplePlanningCalendar to a SAPUI5 App failed with getKey Error

When I add a SimplePlanningCalendar-Control to my app, I got the following Error

I added the calendar with a minimal configuration to my App.

When I debug the app I come to the following line inside the SinglePlanningCalendar.js where a key from the given "vView"-Parameter is requested, but the parameter only holds a String.

Anyone else had this problem before and knows why or how to solve this?

Thank you very much!