Resolving an issue that threw a notice.

git-svn-id: file:///tmp/wdn_thm_drupal/branches/drupal-7.x@94 20a16fea-79d4-4915-8869-1ea9d5ebf173

sites/all/modules/unl/unl_cas.module

@@ -58,7 +58,7 @@ function unl_cas_validate()
 {
 	$cas = unl_cas_get_adapter();
 
-    if ($_POST['logoutRequest']) {
+    if (array_key_exists('logoutRequest', $_POST)) {
         $cas->handleLogoutRequest($_POST['logoutRequest']);
     }