title: param is missing or the value is empty
body: <p>I have two models: <code>Boards</code> and <code>Topics</code>. I want to be able to add <code>Topics</code> to <code>Boards</code>. My nested resources are:</p>
  
  <pre><code>resources :boards do 
      resources :topics
  end
  </code></pre>
  
  <p>My 'boards#show' action:</p>
  
  <pre><code>def show 
      @board = Board.find(params[:id])
      @new_topics = Topic.all
  end
  </code></pre>
  
  <p>which lists all posts and has a <code>link_to</code>:</p>
  
  <pre><code>&lt;ul&gt;
      &lt;%@new_topics.each do |i|%&gt;
          &lt;li&gt;&lt;%=i.title%&gt; &lt;%=link_to "Add", board_topic_path(@board,i), :method=&gt; :put%&gt;&lt;/li&gt;
      &lt;%end%&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>I'm also using strong_params for my <code>Boards</code> and <code>Topics</code> controller as follows:</p>
  
  <p><strong>boards_controller:</strong></p>
  
  <pre><code>def update
      @board = Board.find(params[:board_id])
      @topic = Topic.find(params[:id])        
  
      if @board.update(board_params)
          flash[:notice] = "Added!"
          @board.topics &lt;&lt; @topic
          redirect_to boards_path
  
      else
          flash[:alert] = "Problem!"
          redirect_to boards_path
      end
  
  end
  
  ...
  private
  
  def board_params
      params.require(:board).permit(:name,:description)
  end
  </code></pre>
  
  <p><strong>topics_controller:</strong></p>
  
  <pre><code>...
  private
  
  def topic_params
      params.require(:topic).permit(:title,:body,:user_id)
  end
  </code></pre>
  
  <p>the error message I'm getting: <em>param is missing or the value is empty: topic</em>. </p>