Here is a fix for the problem which arose on my production server when updated_at column was null (because it was just added by a migration). This resulted in exception when a record was updated, because 'index_delta' callback called 'toggled' method for nill column.
I've added the test, but I didn't run it - couldn't setup environment with older rspec.
Thanks for attention,
Fix NPE when new updated_at column was added to existing model and it…
… contains null values