User.create!(name: "James")

ActiveRecord::StatementInvalid: Mysql2::Error: Field 'name' doesn't have a default value: INSERT INTO `users` (`created_at`, `updated_at`, `id`) VALUES ('2014-04-07 12:03:07', '2014-04-07 12:03:07', 980190962)

change_column :users, :name, :string, :limit => 255, :null => false, :default => ''