diff --git a/include/ajax.tickets.php b/include/ajax.tickets.php
index 2a176b9b8c7699010639d54d6dadadb19af36488..be1d0b57e3bdd0e11d37ef6bfb3cfae14772e87b 100644
--- a/include/ajax.tickets.php
+++ b/include/ajax.tickets.php
@@ -1456,7 +1456,7 @@ function refer($tid, $target=null) {
                 && ($f=$iform->getField('duedate'))) {
             $f->configure('max', Misc::db2gmtime($ticket->getEstDueDate()));
         }
-        $vars = array_merge($_SESSION[':form-data'], $vars);
+        $vars = array_merge($_SESSION[':form-data'] ? : array(), $vars);
 
         if ($_POST) {
             Draft::deleteForNamespace(
diff --git a/include/class.thread.php b/include/class.thread.php
index 55be97a108a5fd22eca16543a87df79eab9d2848..7aae4f939bc5dec4ca298b7f1e698f314b556c41 100644
--- a/include/class.thread.php
+++ b/include/class.thread.php
@@ -228,7 +228,7 @@ implements Searchable {
 
             foreach ($vars['cid'] as $c) {
               $collab = Collaborator::lookup($c);
-              if(get_class($collab) == 'Collaborator') {
+              if (($collab instanceof Collaborator)) {
                 $collab->setFlag(Collaborator::FLAG_ACTIVE, true);
                 $collab->save();
               }