What is causing this NoMethodError in Ruby on Rails?

This is the code I have at the end a the create method in

Notes controller

  def create
    @note = Note.new(params[:note])
    @note.user_id = current_user.id
    respond_to do |format|
      if @note.save
        flash[:success] = 'Note was created.'
        # @note.note_type is "Temp" at this point
        if @note.note_type == "Temp"
          p "passed first test"
          redirect_to :controller => :categories, :action => :add_category, :note_id => @note.id, :category => 'temp category'
        else
          format.html { redirect_to(@note) }
          format.xml  { render :xml => @note, :status => :created, :location => @note }
        end
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @note.errors, :status => :unprocessable_entity }
      end
    end
  end

Categories controller

def add_category
    p "in add_category"
end

When it runs, I get the following error. Line 80, where the trace begins, is the respond_to do |format| line:

NoMethodError in NotesController#create 
undefined method `call' for nil:NilClass
/usr/local/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/whiny_nil.rb:52:in `method_missing'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.3.5/lib/action_controller/mime_responds.rb:175:in `respond'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.3.5/lib/action_controller/mime_responds.rb:173:in `each'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.3.5/lib/action_controller/mime_responds.rb:173:in `respond'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.3.5/lib/action_controller/mime_responds.rb:107:in `respond_to'
/Users/benhartney/rails_projects/note_taker/app/controllers/notes_controller.rb:80:in `create'

I've got no idea 开发者_JS百科how to start debugging this error. The console shows the output line "passed first test" from the create action in the Notes controller, but not the "in add_category" output line from the add_category action in the Categories controller. I'm using Rails 2.3.5. Any help would be greatly appreciated. Thanks for reading.

The respond_to method requires you to specify at least one format on the Responder object passed into its block. In the code-path creating your exception, you just call redirect_to, the responder MIME-type preference list is empty, and Rails ends up trying to call the call method on the (non-existent) block for the (non-existent) first type preference.