按照里克的 rails 实践，把 bootstrap 加入到 rails 来。 $ rails -v Rails 4.2.4 $ ruby -v ruby 2.2.3p173 (2015-08-18 revision 51636) [x86_64-linux]

Gemfile

 gem "therubyracer"
 gem "less-rails"
  gem "twitter-bootstrap-rails"

bundle install

rails g scaffold product name price:decimal description:text
···
然后就出现如下错误
`block in <class:Railtie>': undefined method `register_preprocessor' for nil:NilClass (NoMethodError)
        from /home/yzhao/.rvm/gems/ruby-2.2.3/gems/railties-4.2.4/lib/rails/initializable.rb:30:in `instance_exec'
        from /home/yzhao/.rvm/gems/ruby-2.2.3/gems/railties-4.2.4/lib/rails/initializable.rb:30:in `run'
        from /home/yzhao/.rvm/gems/ruby-2.2.3/gems/railties-4.2.4/lib/rails/initializable.rb:55:in `block in run_initializers'
        from /home/yzhao/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/tsort.rb:226:in `block in tsort_each'

gem版本
```ruby
Using less 2.6.0
Using sprockets 3.5.2
Using tilt 2.0.1
Using less-rails 2.7.0
Using libv8 3.16.14.13
Using bundler 1.10.6
Using sprockets-rails 3.0.0
Using rails 4.2.4
Using rdoc 4.2.0
Using ref 2.0.0
Using sass-rails 5.0.4
Using sdoc 0.4.1
Using spring 1.6.0
Using sqlite3 1.3.11
Using therubyracer 0.12.2
Using turbolinks 2.5.3
Using twitter-bootstrap-rails 3.2.2