Columns cannot be null anymore. Bug 5343.

(http://moodle.org/bugs/bug.php?op=show&bugid=5343)

Please document it in coding guidelines!!!

backup/lib.php

@@ -409,7 +409,7 @@ function backup_putid ($backup_unique_code, $table, $old_id, $new_id, $info="")
             $rec->backup_code = $backup_unique_code;
             $rec->table_name = $table;
             $rec->old_id = $old_id;
-            $rec->new_id =$new_id;
+            $rec->new_id = ($new_id === null? 0 : $new_id);
             $rec->info = $info_to_save;
 
             $status = insert_record('backup_ids', $rec, false);