I propose the default migration should make email, encrypted_password, and remember_token :null => false.
:null => false
Thinking we can't really have null: false in the "upgrade existing users table" migration: can't add null remember_token, email, and encrypted_password columns to existing user rows.
Will only apply this to the "new users table" migration.
[#206] Improve data integrity
By default, we want email, encrypted_password, and remember_token to
enforce a NOT NULL constraint.