Fix

Controller/Site/PageAdminController.php

 
     public function createEntity(string $entityFqcn)
     {
-        return $this->get(PageContainer::class)
+        return $this->getPageContainer()
                 ->getFactory()
                 ->setSection($this->get(SectionResolver::class)->getCurrent())
                 ->create();

Field/AssociationField.php

         return $this;
     }
 
+    public function setFilterOnMerchantViaSection(MerchantInterface $merchant): self
+    {
+        $this->queryBuilderParameters['merchantViaSection'] = $merchant;
+
+        return $this;
+    }
+
     public function setFilterOnDevAlias(string $devAlias): self
     {
         $this->queryBuilderParameters['devAlias'] = $devAlias;
                         $qb->andWhereMerchantManyToMany('e', $param['merchantManyToMany']);
                     }
 
+                    if (isset($param['merchantViaSection'])) {
+                        $qb->leftJoin('e.section', 's');
+                        $qb->andWhereMerchant('s', $param['merchantViaSection']);
+                    }
+
                     if (isset($param['status'])) {
                         $qb->andWhere('e.status = :status')->setParameter('status', $param['status']);
                     }