Nested set - problems when creating child item

Hi,

I've created a Model with Better Nested Set, but i'm having problems to create child items

My workflow is: - In the (new) form, i pass the desired parent_id in a hidden field. - In the create action, i create the register and after saving it i use the move_to_child_of method.

Everything works! My only problem is that Rails warns that I can't mass asign the property "parent_id"

How can i avoid this warning? Below is my create action:

def create     @invite = Invite.new(params[:invite])     begin       @parent_invitee = Invite.find_by_id(params[:invite][:parent_id])     rescue Exception => exc         logger.error("Invalid parent_id: #{exc.message}")         render :action => "new"     end     respond_to do |format|       if @invite.save         @invite.move_to_child_of(@parent_invitee.id)         flash[:notice] = 'Invite was successfully created.'         format.html { redirect_to :action => "show" }        ...