The error occurred while evaluating nil.sort_by - ruby-on-rails-3

Question

In my articles_controller I have the follow definition
def index
#tags = Article.tag_counts_on(:keywords) || ''
klass = Article
klass = klass.tagged_with(#keyword) if (#keyword = params[:keyword]).present?
#articles = klass.paginate(:page => params[:page])
#articles = Article.where(:state => '4').paginate(:page => params[:page], :per_page => 10)
respond_to do |format|
format.html # index.html.erb
format.xml { render :xml => #articles }
end
end
and in my views/articles/index.html.erb I have the code:
<% #tags.sort_by(&:count).reverse.each do |k| %>
<% url_opts = {:action => "index", :controller => "articles"}
link_name = "#{k.name} (#{k.count})" %>
<% if #keyword == k.name %>
<%= link_to link_name, url_opts.merge(:keyword => nil), :class => "tag current_tag", :title => "Click again to see all" %>
<% else %>
<%= link_to link_name, url_opts.merge(:keyword => k.name), :class => "tag", :title => "Click to filter by #{k.name}" %>
<% end %>
<% end %>
I use Ruby 1.9.2, Rails 3.0.11 and in Gemfile the gem act-as-taggable-on and the follow code
rails generate acts_as_taggable_on:migration
create tables tags and taggings
In my logs I have this error:
Rendered articles/index.html.erb within layouts/application (57.4ms)
Completed 500 Internal Server Error in 189ms
ActionView::Template::Error (You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.sort_by)
The variable #tags is an Array? and have a nil object?

Answer 1

This error is a common Rails (probably Ruby, actually) confuser that just means #tags was nil when you called the sort_by method ... and I guess the error is trying to be helpful since sort_by is a method of Array.
So, why is #tags nil? Fire up rails console (in your project directory) and execute Article.tag_counts_on('something') -- where 'something' is a keyword.
Perhaps you meant in the first line to get keywords from the params array?
#tags = Article.tag_counts_on(params[:keywords])
Also, you need to handle the case where no tags are found, right?

Answer 2

Finaly the solution for this error for me was: NOT DRY. When add the code from
def index to
def all on articles_controller my problem disapear.
my new articles_controller
def index
#tags = Article.tag_counts_on(:keywords)
klass = Article
klass = klass.tagged_with(#keyword) if (#keyword = params[:keyword]).present?
#articles = klass.where(:state => '4').paginate(:page => params[:page])
respond_to do |format|
format.html # index.html.erb
format.xml { render :xml => #articles }
end
end
def all
#tags = Article.tag_counts_on(:keywords)
klass = Article
klass = klass.tagged_with(#keyword) if (#keyword = params[:keyword]).present?
#articles = klass.where(:state => ['3', '4']).search(params[:search]).order('accepted desc').paginate(:page => params[:page], :per_page => 10)
respond_to do |format|
format.html { render 'index' }
format.xml { render :xml => #articles }
end
end