我刚刚将我们的 GitLab 服务器（CentOS 上的 gitlab-ce 软件包）从 8.5.8 更新到了 8.9.6，但是在进行重新配置时，我遇到了数据库迁移问题。
我已经将完整的跟踪信息放到了 pastebin 上：http: //pastebin.com/W1AvYi2x
任何帮助将不胜感激。
编辑：包括代码，这次我运行了 rake 命令，而不是完全重新配置。
# gitlab-rake db:migrate
== 20160301124843 AddVisibilityLevelToGroups: migrating =======================
-- add_column(:namespaces, :visibility_level, :integer, {:null=>false, :default=>20})
-> 0.0985s
-- add_index(:namespaces, :visibility_level)
-> 0.0057s
-- select_one("SELECT restricted_visibility_levels FROM application_settings ORDER BY id DESC LIMIT 1")
-> 0.0005s
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:
undefined method `<' for nil:NilClass/opt/gitlab/embedded/service/gitlab-rails/db/migrate/20160301124843_add_visibility_level_to_groups.rb:9:in `up'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:611:in `exec_migration'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:592:in `block (2 levels) in migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:591:in `block in migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:292:in `with_connection'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:590:in `migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:768:in `migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:998:in `block in execute_migration_in_transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:1044:in `block in ddl_transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `block in transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/abstract/transaction.rb:184:in `within_new_transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/transactions.rb:220:in `transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:1044:in `ddl_transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:997:in `execute_migration_in_transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:959:in `block in migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:955:in `each'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:955:in `migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:823:in `up'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:801:in `migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/tasks/database_tasks.rb:137:in `migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/railties/databases.rake:44:in `block (2 levels) in <top (required)>'
NoMethodError: undefined method `<' for nil:NilClass
/opt/gitlab/embedded/service/gitlab-rails/db/migrate/20160301124843_add_visibility_level_to_groups.rb:9:in `up'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:611:in `exec_migration'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:592:in `block (2 levels) in migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:591:in `block in migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:292:in `with_connection'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:590:in `migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:768:in `migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:998:in `block in execute_migration_in_transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:1044:in `block in ddl_transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `block in transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/abstract/transaction.rb:184:in `within_new_transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/transactions.rb:220:in `transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:1044:in `ddl_transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:997:in `execute_migration_in_transaction'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:959:in `block in migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:955:in `each'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:955:in `migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:823:in `up'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/migration.rb:801:in `migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/tasks/database_tasks.rb:137:in `migrate'
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.6/lib/active_record/railties/databases.rake:44:in `block (2 levels) in <top (required)>'
Tasks: TOP => db:migrate