Fix for regression from Pull #620
Fix for regression from Pull #620

https://github.com/gitbrent/PptxGenJS/commit/5c6195d196ae35ddd886f1dd7daa05aa84e013de#diff-bcfc646e59f5f5a1fd1e07d3eea51edc

gitbrent/PptxGenJS,gitbrent/PptxGenJS,gitbrent/PptxGenJS