>> User::RandomInvitationsJoiner.new.join_all
NoMethodError: You have a nil object when you didn't expect it!
The error occurred while evaluating nil.description
        from /home/docent/repos/new_klanz/klanz.git/klanz/lib/constraint_provider.rb:143:in `to_str'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/restriction_set.rb:16:in `apply_rules'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/restriction_set.rb:16:in `each'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/restriction_set.rb:16:in `apply_rules'
        from /home/docent/repos/new_klanz/klanz.git/klanz/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:177:in `send'
        from /home/docent/repos/new_klanz/klanz.git/klanz/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:177:in `method_missing'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/room/tournament_hosting.rb:29:in `available_by_restrictions_for?'
        from /home/docent/repos/new_klanz/klanz.git/klanz/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:177:in `send'
        from /home/docent/repos/new_klanz/klanz.git/klanz/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:177:in `method_missing'
        from /home/docent/repos/new_klanz/klanz.git/klanz/lib/invitation_guard.rb:14:in `valid?'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/user/random_invitations_joiner.rb:33:in `can_be_joined?'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/user/random_invitations_joiner.rb:23:in `join_in_room'
        from /home/docent/repos/new_klanz/klanz.git/klanz/vendor/rails/activerecord/lib/active_record/base.rb:1374:in `find'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/user/random_invitations_joiner.rb:23:in `each'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/user/random_invitations_joiner.rb:23:in `find'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/user/random_invitations_joiner.rb:23:in `join_in_room'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/user/random_invitations_joiner.rb:13:in `join_all'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/user/random_invitations_joiner.rb:11:in `each'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/user/random_invitations_joiner.rb:11:in `join_all'
        from /home/docent/repos/new_klanz/klanz.git/klanz/lib/with_lock.rb:27:in `with_lock'
        from /usr/lib/ruby/1.8/timeout.rb:56:in `timeout'
        from /home/docent/repos/new_klanz/klanz.git/klanz/lib/with_lock.rb:27:in `with_lock'
        from /home/docent/repos/new_klanz/klanz.git/klanz/app/models/user/random_invitations_joiner.rb:9:in `join_all'
        from (irb):7
        from :0>>