yii : $model->save() inserts null values when we I have empty rules

yii : $model->save() inserts null values when we I have empty rules

I don't have any rules for the input fields, (name,place, position) so my
model's rules function returns an empty array, but then empty values are
getting saved into the database table.
public function rules()
{
return array();
}
Also when I omit rules() function from my model
$model->save()
returns true but DB table get inserted with empty values.
so how can I omit rules() function from my model class ?