failed add_filter parent_id
On the wiki page there's the parent_id filter that I'd like to use, but I got that there's not a valid filter. Below the environment of my redmine server.
Redmine version 2.6.5.stable.14391
Ruby version 1.9.3-p194 (2012-04-20) [x86_64-linux]
Rails version 3.2.22
Database adapter Mysql2