class RubyXL::Stylesheet

def get_number_format_by_id(format_id)
  @format_hash ||= {}
  
  if @format_hash[format_id].nil? then
    @format_hash[format_id] = NumberFormats::DEFAULT_NUMBER_FORMATS.find_by_format_id(format_id) ||
                                (number_formats && number_formats.find_by_format_id(format_id))
  end
  @format_hash[format_id]
end