Basically the easiest way to achieve this will be to use the edit
event of the Grid.
I tried other approaches however since most probably the column field is of type int (or nullable int) you wont be able to set the default value to be empty string - which is actually the value of the combo when there is "option label". Also if you want this field to be required you will once again need to make the default value empty string.
For simplicity I created a sample project which you can try.
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