diff --git a/Classes/Domain/Model/Import.php b/Classes/Domain/Model/Import.php
index e2295f8..fcb1178 100644
--- a/Classes/Domain/Model/Import.php
+++ b/Classes/Domain/Model/Import.php
@@ -146,9 +146,9 @@ public function setTargetWorkspace($targetWorkspace)
      */
     public function flush()
     {
-        unset($this->data);
-        unset($this->parentNodeIdentifier);
-        unset($this->targetNodeType);
-        unset($this->targetWorkspace);
+        $this->data = null;
+        $this->parentNodeIdentifier = null;
+        $this->targetNodeType = null;
+        $this->targetWorkspace = null;
     }
 }