Object reference error on editing calendar event - SharePoint 2010

Question

I am working on SharePoint 2010 Calendar. By default the Start Date and End Date fields are required in Event Content Type. I made both of these fields optional. When I add an Event to the Calendar, with blank Start and End Date the Event gets saved without any problem. When I edit the Event, do nothing and click on save, exception occurs.

Object reference not set to an instance of an object.

[NullReferenceException: Object reference not set to an instance of an object.]
   Microsoft.SharePoint.WebControls.DateTimeField.GetDateValue(DateTimeField fieldControl) +128
   Microsoft.SharePoint.WebControls.DateTimeField.Validate(Boolean validateMemberControl) +474
   Microsoft.SharePoint.WebControls.DateTimeField.Validate() +44
   System.Web.UI.Page.Validate() +117
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +105
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +29
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2981

I do not have any custom code.

Answer 1

After research and contacting Microsoft support, understand that this is an expected behavior in SharePoint Calendar. Though we can set the Start Date and End Date columns to be optional, we need to fill in the two columns when editing the events.

The following thread is for your reference. Sharepoint 2010 Calendar - Start Date / End Date Blank –