IS NOT NOT不在Yii Active Record中工作

我正在尝试这样的事情:

public function search() {

        $criteria = new CDbCriteria;

        $criteria->compare('user_details_id', $this->user_details_id);
        $criteria->compare('user_type_id', $this->user_type_id);
        $criteria->compare('customer_basics_id', $this->customer_basics_id);
        $criteria->compare('user_address_id', $this->user_address_id);
        $criteria->compare('user_city_id', $this->user_city_id);
        $criteria->compare('is_active', $this->is_active);
        $criteria->compare('create_dttm', $this->create_dttm, true);
        $criteria->compare('update_dttm', $this->update_dttm, true);

        // if condition is working
        if (isset($_GET['ulip'])) {
            $criteria->addCondition(
                    "customer_basics_id=" . CustomerBasics::getCustomerBasicsId(Yii::app()->session['user_id']), "AND"
            );
            $criteria->addCondition("user_city_id IS NULL");
        // else condition is working
        } else {
            $criteria->addCondition(
                    "customer_basics_id=" . CustomerBasics::getCustomerBasicsId(Yii::app()->session['user_id']), "AND"
            );
            $criteria->addCondition("user_city_id IS NOT NULL");
        }


    return new CActiveDataProvider($this, array(
        'criteria' => $criteria,
        'pagination' => array(
            'pageSize' => 10,
        ),
    ));
}

这里的问题是if条件工作正常并根据条件显示结果但是部分不起作用并且它什么都不返回.我认为IS NOT NULL这不起作用.

有什么问题？