Currently, you can select a single day, but this will set the StartDate to the selected date and EndDate to null. Add option to enable a selection range of a single day, where StartDate == EndDate. 
At the moment, you can do that by programmatically setting the StartEnd and EndDate properties, or by editing the values in the text input, but this cannot be done via the UI. 
Also, when StartDate == EndDate, a click on another date in the calendar continues the selection, instead of starting a new selection range. In this situation, a new selection should be started when another date is clicked.