def blank_slate(opts = nil, &block)
      if (opts.is_a?(Hash) && opts.key?(:partial) && block.nil?) || (opts.is_a?(String) && block.nil?)
        @blank_slate_handler = opts
      elsif opts.nil? && block
        @blank_slate_handler = block
      else
        raise WiceGridArgumentError.new("blank_slate accepts only a string, a block, or template: 'path_to_template' ")
      end
    end
def blank_slate(opts = nil, &block)
      if (opts.is_a?(Hash) && opts.key?(:partial) && block.nil?) || (opts.is_a?(String) && block.nil?)
        @blank_slate_handler = opts
      elsif opts.nil? && block
        @blank_slate_handler = block
      else
        raise WiceGridArgumentError.new("blank_slate accepts only a string, a block, or template: 'path_to_template' ")
      end
    end
The output of the block submitted to +blank_slate+ is rendered instead of the whole grid if no filters are active
 and there are no records to render.
 In addition to the block style two other variants are accepted:
 *   <tt>g.blank_slate "some text to be rendered"</tt>
 *   <tt>g.blank_slate partial: "partial_name"</tt>