code: def notes_placeholder(self):
          
          for placeholder in self.placeholders:
              if placeholder.placeholder_format.type == PP_PLACEHOLDER.BODY:
                  return placeholder
          return None
docs: Return the notes placeholder on this notes slide, the shape that
          contains the actual notes text. Return |None| if no notes placeholder
          is present; while this is probably uncommon, it can happen if the
          notes master does not have a body placeholder, or if the notes
          placeholder has been deleted from the notes slide.