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When I change parent issue id, I got internal error.
Here comes the error log:

ArgumentError (comparison of Date with nil failed):
  app/models/issue.rb:801:in `recalculate_attributes_for'
  app/models/issue.rb:759:in `update_nested_set_attributes'
  app/models/issue.rb:599:in `save_issue_with_child_records'
  app/models/issue.rb:581:in `save_issue_with_child_records'
  app/controllers/issues_controller.rb:174:in `update'
  /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

OS:
Ubuntu 10.04
Linux us1 2.6.32-305-ec2 #9-Ubuntu SMP Thu Apr 15 04:14:01 UTC 2010 i686 GNU/Linux

Version:
Redmine 1.2.0.stable.6081 (MySQL)

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