code: def get_item_args(opts)
        opts[:base_shape] ||= 'Default'
        default_args = {
          item_shape: {base_shape: opts[:base_shape]},
          item_ids:   [{item_id:{id: id, change_key: change_key}}]
        }
        default_args[:item_shape][:body_type] = @body_type if @body_type
        default_args
      end
docs: Build up the arguements for #get_item
   @todo: should we really pass the ChangeKey or do we want the freshest obj?