Yii how to ignore empty attributes (null, "") in $criteria->compare()?

Question

Yii

actually, a subject,
for example, I send a form in which not all fields are filled
, then my query string looks like /
activity?
it can be seen that only Activity[responsible_id]=526 is filled, all the rest are empty
when I assign attributes, and then I try to display CGridView (dataProvider=>$model->search()) - empty fields are taken into account in my request, and it does not correctly find data
how to ignore empty fields?
db mysql

Answer 1

if (($_POST['param']) and ($_POST['param']!=''))
//add compare