Error during failsafe response: Couldn't find Track without an ID

I'm wanting to have more dynamic error messages in my custom not_found (404) template. The most common issues are people looking for Artists or Tracks that are no longer in our DB. When an artist or track isn't found, render a specific message.

I get this error:

Error during failsafe response: Couldn't find Track without an ID

I want it to not find the Track or artist in the DB but not break the app. Any idears? The problem is in my custom_404_message method.

application_controller.rb

  def custom_404_message
    artist = Artist.find_by_slug(params[:slug])
    track = Track.find(params[:id])

    if params.has_key? "artists" && artist.nil?
      @message = "It looks like the artist you are looking for is not on our site."
    elsif params.has_key? "tracks" && track.nil?
      @message = "It looks like the song you are looking for is not on our site." 
    else 
     @message = "The page you are looking for does not exist :-("
    end
     @message
  end

errors_controller.rb

  def not_found
    @message = custom_404_message  
    render file: "#{Rails.root}/app/views/errors/not_found.html.erb", layout: false, status: 404
  end

not_found.html.erb

 <div id="content">
      <section id="mm-not-found">
        <header id="mm-not-found-landing">
          <div class="cover-image header-bg" style="background-image: url(//marmoset-music-standard.s3.amazonaws.com/assets/headers/forest-5d7e462b4e278fb7b241a57e654dca5a.jpg); background-size: cover; background-position: 50% 50%; background-repeat: no-repeat no-repeat;"></div>
          <hgroup>
            <div class="contain">
              <div class="error-icon"><span></span></div>
              <h1>Ooops! Sorry for the confusion.</h1>
            </div>
          </hgroup>
        </header>
        <article>
          <div class="contain">
            <h2><%= @message %></h2>
            <em>If you feel like this is a problem on our end, please <a href="/contact" data-bypass="true">contact us</a>.</em>
          </div>
        </article>
      </section>
    </div>
  </div>
</body>
</html>