warning messages from array functions in various places

In several locations, array functions may be called with null arguments where an array is required. This produces a distracting warning message. One good solution is to apply the (array) cast to any array type argument that might be null. Here is a patch against 6.x-1.x-dev (Nov. 25, 08) which suppresses two such messages:

===================================================================
--- formfilter_ui/formfilter_ui.module	(revision 2236)
+++ formfilter_ui/formfilter_ui.module	(working copy)
@@ -90,7 +90,7 @@
   if ((!$_REQUEST['formfilter_id']) && array_key_exists($form_id, $filters) && ((!user_access('view forms without filtering') || $_REQUEST['formfilter_preview']))) {
     $form_filters = array();
     // Convert filters to arrays.
-    foreach (array_keys($filters[$form_id]) as $filter) {
+    foreach ((array)array_keys($filters[$form_id]) as $filter) {
       $form_filters[] = explode('|', $filter);
     }
     if ($_REQUEST['formfilter_preview']) {
@@ -142,7 +142,7 @@
  */
 function formfilter_ui_form_validate($form, &$form_state) {
   $filters = variable_get('formfilter', array());
-  $filters[$form_state['values']['form_id']] = array_filter($_REQUEST['edit']['formfilter']);
+  $filters[$form_state['values']['form_id']] = array_filter((array)$_REQUEST['edit']['formfilter']);
   variable_set('formfilter', $filters);
   drupal_set_message(t('Form filtering registered.'));
   drupal_goto($_GET['q']);