I decided to give the Four Days on Rails documentation another try. I pre-loaded the database using the todos.sql script provided. However, after I followed all the steps up to and including those on page 17 the list categories page (http://localhost:3000/categories/list) errored out:
undefined method `strftime’ for nil:NilClass

I decided that the strftime function might not like the value ‘0000-00-00 00:00:00’ stored in both the create_on and update_on fields. Consequently, I emptied the categories table. Then, the list categories page worked for the no results case. Then, I added a category and the list categories page executed as expected.