Index: category.php
===================================================================
--- category.php (revision 12592)
+++ category.php (working copy)
@@ -178,11 +178,13 @@
  * @since 1.0.0
  *
  * @param int $cat_id Category ID
- * @return string Category name
+ * @return string Category name, or an empty string if category doesn't exist.
  */
 function get_cat_name( $cat_id ) {
         $cat_id = (int) $cat_id;
         $category = &get_category( $cat_id );
+        if ( ! $category || is_wp_error( $category ) )
+                return '';
         return $category->name;
 }