diff --git a/CRM/ManualDirectDebit/Hook/BuildForm/CustomData.php b/CRM/ManualDirectDebit/Hook/BuildForm/CustomData.php
index 9080f9a..49b5291 100644
--- a/CRM/ManualDirectDebit/Hook/BuildForm/CustomData.php
+++ b/CRM/ManualDirectDebit/Hook/BuildForm/CustomData.php
@@ -58,7 +58,8 @@ public function run() {
   private function checkIfDirectDebitMandateInGroupTree() {
     $customGroupTree = $this->form->getVar('_groupTree');
 
-    return array_key_exists($this->directDebitMandateId, $customGroupTree);
+
+    return !empty($customGroupTree) && array_key_exists($this->directDebitMandateId, $customGroupTree);
   }
 
   /**