6 files changed, 16 insertions, 8 deletions
diff --git a/guides/source/active_model_basics.md b/guides/source/active_model_basics.md
index 1d87646e49..0019d08328 100644
--- a/guides/source/active_model_basics.md
+++ b/guides/source/active_model_basics.md
@@ -120,8 +120,8 @@ class Person
   end
 
   def save
-    @previously_changed = changes
     # do save work...
+    changes_applied
   end
 end
 ```
diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md
index c58dd2e90a..8ef982f8c5 100644
--- a/guides/source/association_basics.md
+++ b/guides/source/association_basics.md
@@ -261,7 +261,10 @@ With `through: :sections` specified, Rails will now understand:
 
 ### The `has_one :through` Association
 
-A `has_one :through` association sets up a one-to-one connection with another model. This association indicates that the declaring model can be matched with one instance of another model by proceeding _through_ a third model. For example, if each supplier has one account, and each account is associated with one account history, then the customer model could look like this:
+A `has_one :through` association sets up a one-to-one connection with another model. This association indicates
+that the declaring model can be matched with one instance of another model by proceeding _through_ a third model.
+For example, if each supplier has one account, and each account is associated with one account history, then the
+supplier model could look like this:
 
 ```ruby
 class Supplier < ActiveRecord::Base
diff --git a/guides/source/engines.md b/guides/source/engines.md
index 48d2949539..c71b728ef7 100644
--- a/guides/source/engines.md
+++ b/guides/source/engines.md
@@ -307,7 +307,11 @@ create      test/models/blorgh/comment_test.rb
 create      test/fixtures/blorgh/comments.yml
 ```
 
-This generator call will generate just the necessary model files it needs, namespacing the files under a `blorgh` directory and creating a model class called `Blorgh::Comment`.
+This generator call will generate just the necessary model files it needs, namespacing the files under a `blorgh` directory and creating a model class called `Blorgh::Comment`. Now run the migration to create our blorgh_comments table:
+
+```bash
+$ rake db:migrate
+```
 
 To show the comments on a post, edit `app/views/blorgh/posts/show.html.erb` and add this line before the "Edit" link:
 
diff --git a/guides/source/generators.md b/guides/source/generators.md
index a8a34d0ac4..3df87b84c3 100644
--- a/guides/source/generators.md
+++ b/guides/source/generators.md
@@ -35,7 +35,7 @@ $ rails generate helper --help
 Creating Your First Generator
 -----------------------------
 
-Since Rails 3.0, generators are built on top of [Thor](https://github.com/wycats/thor). Thor provides powerful options parsing and a great API for manipulating files. For instance, let's build a generator that creates an initializer file named `initializer.rb` inside `config/initializers`.
+Since Rails 3.0, generators are built on top of [Thor](https://github.com/erikhuda/thor). Thor provides powerful options parsing and a great API for manipulating files. For instance, let's build a generator that creates an initializer file named `initializer.rb` inside `config/initializers`.
 
 The first step is to create a file at `lib/generators/initializer_generator.rb` with the following content:
 
@@ -47,7 +47,7 @@ class InitializerGenerator < Rails::Generators::Base
 end
 ```
 
-NOTE: `create_file` is a method provided by `Thor::Actions`. Documentation for `create_file` and other Thor methods can be found in [Thor's documentation](http://rdoc.info/github/wycats/thor/master/Thor/Actions.html)
+NOTE: `create_file` is a method provided by `Thor::Actions`. Documentation for `create_file` and other Thor methods can be found in [Thor's documentation](http://rdoc.info/github/erikhuda/thor/master/Thor/Actions.html)
 
 Our new generator is quite simple: it inherits from `Rails::Generators::Base` and has one method definition. When a generator is invoked, each public method in the generator is executed sequentially in the order that it is defined. Finally, we invoke the `create_file` method that will create a file at the given destination with the given content. If you are familiar with the Rails Application Templates API, you'll feel right at home with the new generators API.
 
@@ -422,7 +422,7 @@ Generator methods
 
 The following are methods available for both generators and templates for Rails.
 
-NOTE: Methods provided by Thor are not covered this guide and can be found in [Thor's documentation](http://rdoc.info/github/wycats/thor/master/Thor/Actions.html)
+NOTE: Methods provided by Thor are not covered this guide and can be found in [Thor's documentation](http://rdoc.info/github/erikhuda/thor/master/Thor/Actions.html)
 
 ### `gem`
 
diff --git a/guides/source/getting_started.md b/guides/source/getting_started.md
index e5bc5ef038..d5444af002 100644
--- a/guides/source/getting_started.md
+++ b/guides/source/getting_started.md
@@ -22,8 +22,8 @@ with Rails. However, to get the most out of it, you need to have some
 prerequisites installed:
 
 * The [Ruby](http://www.ruby-lang.org/en/downloads) language version 1.9.3 or newer
-* The [RubyGems](http://rubygems.org/) packaging system
-    * To learn more about RubyGems, please read the [RubyGems User Guide](http://docs.rubygems.org/read/book/1)
+* The [RubyGems](http://rubygems.org) packaging system
+    * To learn more about RubyGems, please read the [RubyGems Guides](http://guides.rubygems.org)
 * A working installation of the [SQLite3 Database](http://www.sqlite.org)
 
 Rails is a web application framework running on the Ruby programming language.
diff --git a/guides/source/migrations.md b/guides/source/migrations.md
index 3c512e0390..1c858069f3 100644
--- a/guides/source/migrations.md
+++ b/guides/source/migrations.md
@@ -301,6 +301,7 @@ braces. You can use the following modifiers:
 * `precision`    Defines the precision for the `decimal` fields
 * `scale`        Defines the scale for the `decimal` fields
 * `polymorphic`  Adds a `type` column for `belongs_to` associations
+* `null`         Allows or disallows `NULL` values in the column.
 
 For instance, running