Undefined index: node in custom_search_preprocess_search_results()

Hi,

In the advanced search, fill the search field with something, and click on the Search button. You are currently in the "Content" tab.
Then go to the "Users" tab, clean the search field then add another text. Click on the Search button.
After the results are displayed, go back to the "Content" tab, or click on one of the results link, and there is this error :

Notice : Undefined index: node dans custom_search_preprocess_search_results() (ligne 36 dans D:\Programmes\wamp\www\KTTN\drupal\sites\all\modules\custom_search\custom_search.pages.inc).
Notice : Trying to get property of non-object dans custom_search_preprocess_search_results() (ligne 36 dans D:\Programmes\wamp\www\KTTN\drupal\sites\all\modules\custom_search\custom_search.pages.inc).

(Sorry for my bad english)