def update_layer
    self.layers.each do |layer|
      layer.create_tileindex
      layer.save_mapfile
    end unless self.layers.empty?
  end

instead of:
  def update_layer
     unless self.layers.empty?
       self.layers.each do |layer|
         layer.create_tileindex
         layer.save_mapfile
       end
     end
   end