def to_xml_string(str = '')
      super(str) do

        colors.each_with_index do |c, index|
          str << '<c:dPt>'
          str << ('<c:idx val="' << index.to_s << '"/>')
          str << '<c:spPr><a:solidFill>'
          str << ('<a:srgbClr val="' << c << '"/>')
          str << '</a:solidFill></c:spPr></c:dPt>'
        end

        @labels.to_xml_string(str) unless @labels.nil?
        @data.to_xml_string(str) unless @data.nil?
        # this is actually only required for shapes other than box 
        str << ('<c:shape val="' << shape.to_s << '"></c:shape>')
      end
    end
def to_xml_string(str = '')
      super(str) do

        colors.each_with_index do |c, index|
          str << '<c:dPt>'
          str << ('<c:idx val="' << index.to_s << '"/>')
          str << '<c:spPr><a:solidFill>'
          str << ('<a:srgbClr val="' << c << '"/>')
          str << '</a:solidFill></c:spPr></c:dPt>'
        end

        @labels.to_xml_string(str) unless @labels.nil?
        @data.to_xml_string(str) unless @data.nil?
        # this is actually only required for shapes other than box 
        str << ('<c:shape val="' << shape.to_s << '"></c:shape>')
      end
    end
Serializes the object
 @param [String] str
 @return [String]