- Fixed nullable errors after forced typing

src/Handler.php

@@ -13,7 +13,7 @@ abstract class Handler {
     
     public bool $registerFatalErrorHandler = true;
 
-    protected Closure $callback;
+    protected ? Closure $callback;
 
     protected Transport\TransportInterface $transport;
    

src/Util/DumpHandler.php

@@ -6,7 +6,7 @@ use Negundo\Client\DataInterface;
 
 class DumpHandler {
 
-    public DataInterface $dataManipulator;
+    public ? DataInterface $dataManipulator;
 
     public function __construct(DataInterface $dataManipulator = null)
     {

src/Util/TaskHandler.php

@@ -6,7 +6,7 @@ use Negundo\Client\DataInterface;
 
 class TaskHandler {
 
-    public DataInterface $dataManipulator;
+    public ? DataInterface $dataManipulator;
 
     public function __construct(DataInterface $dataManipulator = null)
     {