public function whereNull($col, $and = true, $not = false)
    {
        return $this->where($col, $not ? 'IS NOT NULL' : 'IS NULL',
            WhereInterface::SHORT_FORM, $and);
    }
public function whereNull($col, $and = true, $not = false)
    {
        return $this->where($col, $not ? 'IS NOT NULL' : 'IS NULL',
            WhereInterface::SHORT_FORM, $and);
    }
{@inheritDoc}