answer is not so simple, because cb is connected to database and user should be able to update value with "null".
Now I am using below method, but I was trying to find something similar to RadGrid DropDown "EnableEmptyListItem" .
I would suggest you to use the Default Item of the RadComboBox. Here you could find our documentation article regarding the usage of the Default Item. Please note, that it could be implemented only in a readonly RadComboBox scenario.
Regards,
Nencho
Telerik
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