winforms - Check for null via BinaryOperator -

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groupoperator groupapplyon = new groupoperator();          groupapplyon.operatortype = groupoperatortype.and;         groupapplyon.operands.add(isb);         groupapplyon.operands.add(isa);         groupapplyon.operands.add(isc);

where isx binaryoperator .. 

binaryoperator isb = new binaryoperator("validity", null,             binaryoperatortype.equal);

this code gives me error - how check public unaryoperator isnull() if "validity" null?

use nulloperator instead.


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