attachment_fu file upload optional in 'new' view?

In my 'new' view for an Item object, the user can upload a picture of
the item. How can I make the upload optional (while creating the new
item)? I'm using REST and this is a portion of what my controller
looks like to make it Mandatory to upload an image:

respond_to do |format|
      if @item.save and @photo.save

Now if I remove the @photo.save no image will be created (even if it
is valid).

Okay I figured it out. I assigned the @photo to @item:
@item.photo = @photo

then:
respond_to do |format|
    if @item.save

Attachment_fu is a great plugin!