Binding an MVVM DropDownList to null data produces an error

### Bug report

Binding an MVVM DropDownList to a property that is null results in an error on the console.

### Reproduction of the problem

1. Open this example - https://dojo.telerik.com/@sspasova/AMIwIBUd

### Current behavior
An error is thrown

### Expected/desired behavior
No errors should be thrown

### Environment

* **Kendo UI version:** 2023.3.1114
* **Browser:** [all] 


