internal error when trying to access some issues (Bug #639)

When attempting to show certain issues the following backtrace is printed in the log:

Processing IssuesController#show (for 192.168.10.32 at 2011-09-23 12:38:23) [GET]
Parameters: {"action"=>"show", "id"=>"942", "controller"=>"issues"}
Rendering template within layouts/base
Rendering issues/show.rhtml

ActionView::TemplateError (undefined method `name' for nil:NilClass) on line #2 of app/views/issues/_history.rhtml:
1: <% for journal in journals >
2: <%= render_journal issue, journal, :edit_permission => :edit_issue_notes,
3: :edit_own_permission => :edit_own_issue_notes %>
4: <%= call_hook(:view_issues_history_journal_bottom, { :journal => journal }) %>
5: < end %>

app/helpers/journals_helper.rb:48:in `render_journal_details'
    app/helpers/journals_helper.rb:47:in `each'
    app/helpers/journals_helper.rb:47:in `collect'
    app/helpers/journals_helper.rb:47:in `render_journal_details'
    app/helpers/journals_helper.rb:46:in `render_journal_details'
    app/helpers/journals_helper.rb:29:in `render_journal'
    app/views/issues/_history.rhtml:2:in `_run_rhtml_app47views47issues47_history46rhtml_locals_history_issue_journals_object'
    app/views/issues/_history.rhtml:1:in `each'
    app/views/issues/_history.rhtml:1:in `_run_rhtml_app47views47issues47_history46rhtml_locals_history_issue_journals_object'
    app/views/issues/show.rhtml:95:in `_run_rhtml_app47views47issues47show46rhtml'
    app/controllers/issues_controller.rb:102:in `show'
    app/controllers/issues_controller.rb:101:in `show'
    /usr/lib/ruby/1.8/phusion_passenger/rack/request_handler.rb:92:in `process_request'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_request_handler.rb:207:in `main_loop'
    /usr/lib/ruby/1.8/phusion_passenger/railz/application_spawner.rb:418:in `start_request_handler'
    /usr/lib/ruby/1.8/phusion_passenger/railz/application_spawner.rb:358:in `handle_spawn_application'
    /usr/lib/ruby/1.8/phusion_passenger/utils.rb:184:in `safe_fork'
    /usr/lib/ruby/1.8/phusion_passenger/railz/application_spawner.rb:354:in `handle_spawn_application'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_server.rb:352:in `__send__'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_server.rb:352:in `main_loop'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_server.rb:196:in `start_synchronously'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_server.rb:163:in `start'
    /usr/lib/ruby/1.8/phusion_passenger/railz/application_spawner.rb:213:in `start'
    /usr/lib/ruby/1.8/phusion_passenger/spawn_manager.rb:262:in `spawn_rails_application'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_server_collection.rb:126:in `lookup_or_add'
    /usr/lib/ruby/1.8/phusion_passenger/spawn_manager.rb:256:in `spawn_rails_application'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_server_collection.rb:80:in `synchronize'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_server_collection.rb:79:in `synchronize'
    /usr/lib/ruby/1.8/phusion_passenger/spawn_manager.rb:255:in `spawn_rails_application'
    /usr/lib/ruby/1.8/phusion_passenger/spawn_manager.rb:154:in `spawn_application'
    /usr/lib/ruby/1.8/phusion_passenger/spawn_manager.rb:287:in `handle_spawn_application'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_server.rb:352:in `__send__'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_server.rb:352:in `main_loop'
    /usr/lib/ruby/1.8/phusion_passenger/abstract_server.rb:196:in `start_synchronously'
    /usr/lib/phusion_passenger/passenger-spawn-server:61

Rendering /var/chiliproject-git/public/500.html (500 Internal Server Error)

Here are two DB entries for a working (id=943) and not working (id=942) issue in case there is some problem with the DB:
id tracker_id project_id due_date category_id status_id assigned_to_id priority_id fixed_version_id author_id lock_version created_on updated_on start_date done_ratio estimated_hours parent_id root_id lft rgt
942 2 4 2011-09-30 NULL 2 5 5 NULL 5 13 2011-08-19 17:25:08 2011-09-23 12:39:23 2011-08-19 20 NULL 931 931 6 7
943 5 4 NULL NULL 5 2 3 NULL 2 5 2011-08-22 11:49:45 2011-09-23 13:31:06 2011-08-22 0 NULL NULL 943 1 2

The issues come from a recent migration from trac to chiliproject.
Please let me know if you need further info to analyze the problem.