added nullpointer check

Author: BowlingX

lib/Gedmo/Tree/Strategy/ORM/MaterializedPath.php

@@ -23,18 +23,21 @@ public function removeNode($om, $meta, $config, $node)
         $wrapped = AbstractWrapper::wrap($node, $om);
 
         $path = addcslashes($wrapped->getPropertyValue($config['path']), '%');
-        $lvl = $wrapped->getPropertyValue($config['level']);
 
         // Remove node's children
         $qb = $om->createQueryBuilder();
         $qb->select('e')
             ->from($config['useObjectClass'], 'e')
             ->where($qb->expr()->like('e.'.$config['path'], $qb->expr()->literal($path.'%')));
-        
-        if(!empty($lvl) && $meta->hasField($config['level'])){
-            $qb->andWhere($qb->expr()->gt('e.'.$config['level'], $qb->expr()->literal($lvl)));
+
+        if (isset($config['level'])) {
+            $lvlField = $config['level'];
+            $lvl = $wrapped->getPropertyValue($lvlField);
+            if (!empty($lvl) && $meta->hasField($lvlField)) {
+                $qb->andWhere($qb->expr()->gt('e.' . $lvlField, $qb->expr()->literal($lvl)));
+            }
         }
-        
+
         $results = $qb->getQuery()
             ->execute();