Index: wp-admin/includes/plugin.php
===================================================================
--- wp-admin/includes/plugin.php	(revision 5773)
+++ wp-admin/includes/plugin.php	(working copy)
@@ -291,7 +291,7 @@
 	if ( isset( $wp_filter[$hook] ))
 		return $hook;
 	else
-		return '';
+		return null;
 }
 
 function get_plugin_page_hookname( $plugin_page, $parent_page ) {
@@ -377,4 +377,4 @@
 	return true;
 }
 
-?>
\ No newline at end of file
+?>