I have gotten a great deal of help from KandadaBoggu on my last question and very very thankful for that. As we were getting buried in the comments I wanted to break this part out.

I am attempting to create a tag feature on the rails blog I am developing. The relationship is Post has_many :tags and Tag belongs_to :post. Adding and deleting tags to posts are working great.

In my /view/posts/index.html.erb I have a section called tags where I am successfully querying the Tags table, grouping them and displaying the count next to the tag_name (as a side note, I mistakenly called the column containing the tag name, 'tag_name' instead of just 'name' as I should have) . In addition the display of these groups are a link that is referencing the index method in the PostsController. That is where the problem is.

When you navigate to /posts you get an error because there is no parameter being passed (without clicking the tag group link). I have the .empty? in there so not sure what is going wrong here. Here is the error and code:

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.empty?

/views/posts/index.html.erb

<% @tag_counts.each do |tag_name, tag_count| %> 
            <tr>
                <td><%= link_to(tag_name, posts_path(:tag_name => tag_name)) %></td>
                <td>(<%=tag_count%>)</td>
            </tr>
        <% end %>

PostsController

  def index
    @tag_counts = Tag.count(:group => :tag_name, :order => 'updated_at DESC', :limit => 10)
    @posts=Post.all(:joins => :tags,:conditions=>(params[:tag_name].empty? ? {}: 
                     { :tags => { :tag_name => params[:tag_name] }}
                     )
                  )

    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @posts }
      format.json { render :json => @posts }
      format.atom
    end
  end