Enhancement 

FIltering a string field in the Grid with Contains operators and value null throws an error
Reported in 1492459

Current behavior
FIltering a string field in the Grid with Contains operators and value null throws an error

https://demos.telerik.com/aspnet-mvc/grid/remote-data-binding

Expected/desired behavior
An error shall not be thrown

Environment
Kendo UI version: [all]
Browser: [all]