Index: units/helpers/search_helper.php
===================================================================
--- units/helpers/search_helper.php	(revision 14516)
+++ units/helpers/search_helper.php	(working copy)
@@ -459,7 +459,7 @@
 			}
 
 			$custom_filters = unserialize($custom_filters);
-			if (!array_key_exists($grid_name, $custom_filters)) {
+			if (!is_array($custom_filters) || !array_key_exists($grid_name, $custom_filters)) {
 				// filters not defined for given grid
 				$cache[$cache_key] = false;
 				return false;