Use NullFill pagination adapter instead of Null that is deprecated.

module/VuFind/src/VuFind/Search/Base/Results.php

@@ -463,7 +463,7 @@ abstract class Results implements ServiceLocatorAwareInterface
         }
 
         // Build the standard paginator control:
-        $nullAdapter = "Zend\Paginator\Adapter\Null";
+        $nullAdapter = "Zend\Paginator\Adapter\NullFill";
         $paginator = new Paginator(new $nullAdapter($total));
         $paginator->setCurrentPageNumber($this->getParams()->getPage())
             ->setItemCountPerPage($this->getParams()->getLimit())
@@ -621,4 +621,4 @@ abstract class Results implements ServiceLocatorAwareInterface
             [$this->getOptions(), 'translate'], func_get_args()
         );
     }
-}
+}
\ No newline at end of file