/** * Creates an instance of binary expression node, representing the construction: subject IS NULL * * @param mixed $subject logical subject * * SQL example: * @code * // "id" IS NULL * Expression::isNull("id"); * @endcode * @return UnaryPostfixExpression */ static function isNull($subject) { return new UnaryPostfixExpression($subject, UnaryPostfixLogicalOperator::isNull()); }