Grid advance filter condition selection

How do I exclude the chosen value from an advanced column filter? I want to avoid filters that include null or empty values.

The reason for excluding these is because I get null propagation error in Dynamic linq
Error: " 'np' (null-propagation) function requires the first argument to be a MemberExpression, ParameterExpression or MethodCallExpression linq"

Check MyCustomDataGridColumn in this demo:

Thanks for the quick response. Resolved.