--- og_user_roles.module.orig	2009-07-23 10:04:35.000000000 +0200
+++ og_user_roles.module	2009-07-23 10:12:21.000000000 +0200
@@ -2173,7 +2173,7 @@ function og_user_roles_all_roles($user) 
   $ref = $_SERVER['HTTP_REFERER'];
   $ref_url = parse_url($ref);
   $ref_path = $ref_url['path'];
-  $ref_query = $ref_url['query'];
+  $ref_query = isset($ref_url['query']) ? $ref_url['query'] : '';
   $ref_arg = explode('/', $ref_path);
 
   //
@@ -2186,7 +2186,7 @@ function og_user_roles_all_roles($user) 
 //  require_once("modules/og/og.module");
 
   $group_node = og_get_group_context();
-  $gid02 = $group_node->nid;
+  $gid02 = isset($group_node->nid) ? $group_node->nid : NULL;
   $gid = $gid02;
   if ($gid02 === NULL) {
     $gid = 0;
@@ -3422,7 +3422,7 @@ function og_user_roles_form_alter(&$form
   // the user has the 'auto assign group roles' permission, and we allow group admins
   // to set default group roles, then print the 'basicgrouprole' form on the
   // group edit form.
-  if (arg(0) == 'node' && ($_SESSION['og_last'] == arg(1)) && arg(2) == 'edit' && user_access('auto assign group roles') && variable_get('og_user_roles_assign_basicgrouprole_gid', 0) == 1) {
+  if (arg(0) == 'node' && (isset($_SESSION['og_last']) && $_SESSION['og_last'] == arg(1)) && arg(2) == 'edit' && user_access('auto assign group roles') && variable_get('og_user_roles_assign_basicgrouprole_gid', 0) == 1) {
     $gid = arg(1);
 
     // First, we need to get a list of all og-enabled node types
@@ -3465,7 +3465,7 @@ function og_user_roles_form_alter(&$form
   }
 
   // If this is a group node edit (use og_last to determine if this is a group node) 
-  if (arg(0) == 'node' && ($_SESSION['og_last'] == arg(1)) && arg(2) == 'edit' ) {
+  if (arg(0) == 'node' && (isset($_SESSION['og_last']) && $_SESSION['og_last'] == arg(1)) && arg(2) == 'edit' ) {
     $gid = arg(1);
 
     // First, we need to get a list of all og-enabled node types
@@ -3710,7 +3710,7 @@ function og_user_roles_determine_context
   global $custom_theme;
   $group_node = NULL; // a node object containing the 'active' group for this request
 
-  $type = $_GET['type'];
+  $type = isset($_GET['type']) ? $_GET['type'] : NULL;
 
   if (arg(0) == 'og' && is_numeric(arg(2))) {
     $group_node = og_set_theme(arg(2));
@@ -3765,7 +3765,7 @@ function og_user_roles_determine_context
  */
 function og_user_roles_link_alter(&$links, $node) {
   $node = og_get_group_context();
-  if ($node->nid) {
+  if (isset($node->nid) && $node->nid) {
     $gid = $node->nid;
     foreach ($links as $type => $link) {
       if ($type == 'book_add_child') $links['book_add_child']['query'] .= '&gids[]='.$gid;
@@ -3855,7 +3855,7 @@ function og_user_roles_block($op = 'list
 		}
         break;
     }
-    return $block;
+    return isset($block) ? $block : NULL;
   }
 }
 
@@ -4217,4 +4217,4 @@ function og_user_roles_list_users_sql($m
   return "SELECT u.uid, u.name, u.mail, u.picture, ou.* FROM {og_uid} ou INNER JOIN {users} u ON ou.uid = u.uid WHERE ou.nid = %d AND u.status > 0 AND ou.is_active >= $min_is_active AND ou.is_admin >= $min_is_admin ORDER BY $orderby";
 }
 
-?>
\ No newline at end of file
+?>