Addded additional checking for nestedFilter

Sort/Sort.php

@@ -32,7 +32,9 @@ class Sort extends AbstractSort
     public function __construct($field, $order = self::ORDER_ASC, BuilderInterface $nestedFilter = null, $mode = null)
     {
         parent::__construct($field, $order, $mode);
-        $this->setNestedFilter($nestedFilter);
+        if ($nestedFilter) {
+            $this->setNestedFilter($nestedFilter);
+        }
     }
 
     /**