Create and return a new notes slide part that is fully related, but
        has no shape content (i.e. placeholders not cloned).

def _add_notes_slide_part(cls, package, slide_part, notes_master_part):
        """
        Create and return a new notes slide part that is fully related, but
        has no shape content (i.e. placeholders not cloned).
        """
        partname = package.next_partname('/ppt/notesSlides/notesSlide%d.xml')
        content_type = CT.PML_NOTES_SLIDE
        notes = CT_NotesSlide.new()
        notes_slide_part = NotesSlidePart(
            partname, content_type, notes, package
        )
        notes_slide_part.relate_to(notes_master_part, RT.NOTES_MASTER)
        notes_slide_part.relate_to(slide_part, RT.SLIDE)
        return notes_slide_part