message: Preserving backward compatibility. Data line shadow is visible by default.
diff: @@ -917,8 +917,6 @@ var PptxGenJS = function(){
  * @see http://officeopenxml.com/drwSp-effects.php
  */
  function createShadowElement(opts, defaults) {
  - if (!opts) return '';
  -
  var type = ( opts.type || defaults.type ),
  blur = ( opts.blur || defaults.blur ) * ONEPT,
  offset = ( opts.offset || defaults.offset ) * ONEPT,
  @@ -942,7 +940,7 @@ var PptxGenJS = function(){
  * @param {Object} shadowOpts
  */
  function correctShadowOptions(shadowOpts) {
  - if ( !shadowOpts ) return;
  + if ( !shadowOpts || shadowOpts === 'none' ) return;
  // OPT: `type`
  if ( shadowOpts.type != 'outer' && shadowOpts.type != 'inner' ) {
  console.warn('Warning: shadow.type options are `outer` or `inner`.');
  @@ -1099,9 +1097,9 @@ var PptxGenJS = function(){
  else if ( rel.opts.dataBorder ) {
  strXml += '<a:ln w="'+ (rel.opts.dataBorder.pt * ONEPT) +'" cap="flat"><a:solidFill><a:srgbClr val="'+ rel.opts.dataBorder.color +'"/></a:solidFill><a:prstDash val="solid"/><a:round/></a:ln>';
  }
  - if ( rel.opts.lineShadow ) {
  + if ( rel.opts.lineShadow !== 'none' ) {
  strXml += '<a:effectLst>';
  - strXml += createShadowElement(rel.opts.lineShadow, CHART_LINE_SHADOW_DEFAULTS);
  + strXml += createShadowElement(rel.opts.lineShadow || {}, CHART_LINE_SHADOW_DEFAULTS);
  strXml += '</a:effectLst>';
  }
  strXml += ' </c:spPr>';
  