fix: correctly implement abstract methods in filter handler

src/Service/Common/AbstractFilterHandler.php

@@ -11,7 +11,12 @@ use Symfony\Component\HttpFoundation\Session\SessionInterface;
 abstract class AbstractFilterHandler
 {
     protected string $namespace = 'filter:default';
-    protected string $modelClass = AbstractFilterDto::class;
+
+    /**
+     * The DTO a subclass builds. No default: AbstractFilterDto is abstract, so any value here
+     * would only fatal on instantiation - every handler declares its own.
+     */
+    protected string $modelClass;
 
     public function __construct(
         protected readonly RequestStack $requestStack,
@@ -29,6 +34,8 @@ abstract class AbstractFilterHandler
     public function setModelClass(string $modelClass): static
     {
         $this->modelClass = $modelClass;
+
+        return $this;
     }
 
     public function handleRequest(FormInterface $form): AbstractFilterDto
@@ -50,13 +57,9 @@ abstract class AbstractFilterHandler
         $this->getSession()->remove($this->namespace);
     }
 
-    public function getFilterSettings(): AbstractFilterDto
-    {
-    }
+    abstract public function getFilterSettings(): AbstractFilterDto;
 
-    protected function saveFilterSettings(AbstractFilterDto $filterDto): void
-    {
-    }
+    abstract protected function saveFilterSettings(AbstractFilterDto $filterDto): void;
 
     protected function getSession(): SessionInterface
     {