1 files changed, 5 insertions, 4 deletions
diff --git a/lib/kolab_sync_backend.php b/lib/kolab_sync_backend.php
index 56a411d..a1c24a8 100644
--- a/lib/kolab_sync_backend.php
+++ b/lib/kolab_sync_backend.php
@@ -790,7 +790,7 @@ class kolab_sync_backend
         // get all folders of specified type
         $folderdata = $this->folder_meta();
 
-        if (!is_array($folderdata)) {
+        if (!is_array($folderdata) || $id === null) {
             return null;
         }
 
@@ -802,10 +802,11 @@ class kolab_sync_backend
                 continue;
             }
 
-            $uid = self::folder_id($folder);
-            $this->folder_uids[$folder] = $uid;
+            if ($uid = self::folder_id($folder)) {
+                $this->folder_uids[$folder] = $uid;
+            }
 
-            if ($uid == $id) {
+            if ($uid === $id) {
                 $name = $folder;
             }
         }