Software » Web » Redmine plugins » Scrum

Hi everyone, since a few weeks i've got a error 500 when i create issues.
Here is the log

Completed 500 Internal Server Error in 64ms (ActiveRecord: 9.8ms)

NoMethodError (undefined method `>' for nil:NilClass):
  plugins/scrum/lib/scrum/issue_patch.rb:407:in `block in max_position'
  plugins/scrum/lib/scrum/issue_patch.rb:406:in `each'
  plugins/scrum/lib/scrum/issue_patch.rb:406:in `max_position'
  plugins/scrum/lib/scrum/issue_patch.rb:419:in `move_issue_to_the_end_of_the_sp                                                                                                              rint'
  plugins/scrum/lib/scrum/issue_patch.rb:336:in `update_position'
  app/models/issue.rb:210:in `create_or_update'
  app/controllers/issues_controller.rb:140:in `create'
  lib/redmine/sudo_mode.rb:63:in `sudo_mode'

Any idea?

PS : some info on my redmine instance
Environment:
Redmine version 3.3.2.stable
Ruby version 2.3.1-p112 (2016-04-26) [x86_64-linux]
Rails version 4.2.7.1
Environment production
Database adapter Mysql2
SCM:
Subversion 1.8.10
Git 2.1.4
Filesystem
Redmine plugins:
clipboard_image_paste 1.10
easy_gantt 1.7
redmine_agile 1.4.2
redmine_lightbox2 0.3.1
scrum 0.16.2