Forum: fix error when value is null, it should now be to avoid the error due to commit ea334a3f6f - refs BT#21566

main/forum/forumfunction.inc.php

@@ -436,8 +436,8 @@ function show_add_forum_form($inputvalues = [], $lp_id = 0)
     } else {
         // the default values when editing = the data in the table
         $defaults['forum_id'] = isset($inputvalues['forum_id']) ? $inputvalues['forum_id'] : null;
-        $defaults['forum_title'] = prepare4display(isset($inputvalues['forum_title']) ? $inputvalues['forum_title'] : null);
-        $defaults['forum_comment'] = prepare4display(isset($inputvalues['forum_comment']) ? $inputvalues['forum_comment'] : null);
+        $defaults['forum_title'] = prepare4display(isset($inputvalues['forum_title']) ? $inputvalues['forum_title'] : "");
+        $defaults['forum_comment'] = prepare4display(isset($inputvalues['forum_comment']) ? $inputvalues['forum_comment'] : "");
         $defaults['start_time'] = isset($inputvalues['start_time']) ? api_get_local_time($inputvalues['start_time']) : null;
         $defaults['end_time'] = isset($inputvalues['end_time']) ? api_get_local_time($inputvalues['end_time']) : null;
         $defaults['moderated']['moderated'] = isset($inputvalues['moderated']) ? $inputvalues['moderated'] : 0;