Multiple possibilities for NullPointerException in PowerPointMetadataReader

Missing "Notes" in a sequenced PowerPoint file will cause a NullPointerException to be thrown in PowerPointMetadataReader, and sequence process will be aborted. A null check should be exists for slide.getNotesSheet()

Also, some Office files have a blank "Last Printed" property. A null check should be done before setting this property on sequenced node:

if(null != metadata.getLastPrinted()){
  rootNode.setProperty(LAST_PRINTED, valueFactory.createValue(metadata.getLastPrinted()));
}