ViewModel and KendoUI datasource model

[blazextreme]

I created a ViewModel as below\[code\]public partial class TimeEntryViewModel{ public ActivityCodeViewModel ActivityCode { get; set; } public TimesheetViewModel Timesheet { get; set; } }\[/code\]And now every time i submit a new record from my kendoui grid back to server, it comes with ModelState (that contain error). That means KendoUI datasource model is expecting data for "ActivityCode". My question is how do i let KendoUI know that field is nullable?I'm using KendoUI ASP wrapper. If possible i prefer adding data annotation at the view model declaration.