undefined method visitor

[jspooner]

We're using the mysql2 gem and we noticed this error when we arel updated to 2.1.5. We went back to 2.1.4 and everything went back to normal.

undefined method `visitor' for #ActiveRecord::ConnectionAdapters::Mysql2Adapter:0x00000103dea3d8

http://stackoverflow.com/questions/7001479/undefined-method-visitor-for-rails-3-dbmigrate/7010671#7010671