title: Image will not save with Paperclip and Rails 4
body: <p>I'm trying to use Paperclip for uploading an image for an has many and belongs to relationship with 'pictures'</p>
  
  <p>I'm certain that imagemagick etc, is correctly installed, because i've more image uploaders in this project that works, difference is that this one has an has many relation. </p>
  
  <p>I'm not getting a 'Saving Attachment' in the console. So my idea is that this is completely ignored by the strong parameters. </p>
  
  <p>In topicscontroller: </p>
  
  <pre><code>params.require(:topic).permit(:id, :title, :content, :active, pictures_attributes: [:image, :id, :_destroy] )
  </code></pre>
  
  <p>In Topic Model:</p>
  
  <pre><code>has_many :pictures, dependent: :destroy
  accepts_nested_attributes_for :pictures, allow_destroy: true
  validates :title, :content, presence: true
  </code></pre>
  
  <p>In Picture Model: </p>
  
  <pre><code>belongs_to :topic
  
  has_attached_file :image,
  :styles =&gt; { :medium =&gt; "400x400#", :thumb =&gt; "200x200#", :small =&gt; "50x50#" },
  :default_url =&gt; ActionController::Base.helpers.asset_path('missing.png')
  </code></pre>
  
  <p>I know that there are many other topics about this, only all are rails 3 and is different in the way of setting 'attr_accessible'</p>