I'm new at this so I'm hoping one of you can point me in the right direction to troubleshoot this problem. On page 240, I get an error running the "rake db:migrate" command. As you can see from the trace below,

You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.first


the error seems to be a missing element. How should I go about finding what array is missing, assuming that's the problem?

Thanks for the help.


Full Trace

[ahale@s1bwayapp1 shovell]$ rake db:migrate --trace
(in /home/ahale/shovell)
** Invoke db:migrate (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute db:migrate
rake aborted!
You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.first
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/migration.rb:360:in `migration_files'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/connection_adapters/mysql_adapter.rb:248:in `sort_by'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/migration.rb:359:in `each'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/migration.rb:359:in `sort_by'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/migration.rb:359:in `migration_files'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/migration.rb:342:in `migration_classes'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/migration.rb:330:in `migrate'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/migration.rb:297:in `up'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/migration.rb:288:in `migrate'
/usr/local/lib/ruby/gems/1.8/gems/rails-1.2.3/lib/tasks/databases.rake:4
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:392:in `call'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:392:in `execute'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:392:in `each'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:392:in `execute'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:362:in `invoke'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:355:in `synchronize'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:355:in `invoke'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:1739:in `top_level'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:1739:in `each'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:1739:in `top_level'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:1761:in `standard_exception_handling'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:1733:in `top_level'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:1711:in `run'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:1761:in `standard_exception_handling'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/lib/rake.rb:1708:in `run'
/usr/local/lib/ruby/gems/1.8/gems/rake-0.7.3/bin/rake:7
/usr/local/bin/rake:16:in `load'
/usr/local/bin/rake:16


Versions

[ahale@s1bwayapp1 shovell]$ ruby script/about
About your application's environment
Ruby version 1.8.6 (i686-linux)
RubyGems version 0.9.1
Rails version 1.2.3
Active Record version 1.15.3
Action Pack version 1.13.3
Action Web Service version 1.2.3
Action Mailer version 1.3.3
Active Support version 1.4.2
Application root /home/ahale/shovell
Environment development
Database adapter mysql
Database schema version 3