Laravel WhereNotIn takes null. WhereIn with NULL.

I have a list of categories to which a post may belong. A post category may also be NULL.

//Client model
private $notSaleSections = ['ТПМ-УПП', 'ТПМ-МДФ'];
public function saleParams()
    {
        return $this->hasMany(ClientParameter::class, 'customer', 'id')
            ->whereHas('param', function ($q) {
                $q->where('section', null);
                
                foreach ($this->notSaleSections as $s){
                    $q->orWhere('section', '!=', $s);
                }
            });
    }
    
//ClientParameter model relation to self? you can use other relation
public function param(){
        return $this->hasOne($this, 'id', 'id');
    }