I'd like to use Between and NotBetween operators in the Filter component similar to the available functionality for Telerik UI for AJAX.

Bug report

When a user creates a filter with a date, it starts as an empty Datepicker, but the value is appearing as an empty string. Thus, if the user clicks apply, an error appears in the console. If you place a value in the DatePicker and clear it, the value will be Null.

Reproduction of the problem

1. Go to this Progress Telerik ASP.NET Core REPL.
2. Add filter for a Date but keep the datepicker empty.
3. Select apply.
4. Now, add a date and clear the value.

Current behavior

The filter menu sends isnull filter queries in the following format:

While the Filter component sends it as follows:

As a result the ToDataSourceResult method fails.

Expected/desired behavior

If the DatePicker is empty, the filter should properly perform the 'isnull' query upon clicking apply.

Environment

• Kendo UI version: 2023.2.606
• jQuery version: All Supported Versions
• Browser: all

Feature Enhancement
Expose Default Operator for Filter fields

Current behavior
Apart from setting FilterExpression to render filed with a certain operator, there is no option for setting a Default Operator for the fields

.FilterExpression(f =>
      {
          f.Add(p => p.FirstName).Contains("Jeremy");
      })

The above renders the Contains operator initially but if you change the field and return back to the FirstName field the operator is no longer Contains.

Expected/desired behavior
Default Operator for FIlter fields shall be exposed

Environment
Kendo UI version: all
Browser: al