# File lib/prawn/graph.rb, line 44
    def bar_chart(data, options = {})
      if data.nil? || data.empty?
        raise Prawn::Errors::NoGraphData,
          "data must be a non-empty, non-nil, two dimensional array " +
          "in the form [ [ 'Title', SomeValue ]  ]"
      end
      Prawn::Chart::Bar.new(data, self, options).draw
    end