code: def _connect_end_to(self, shape, cxn_pt_idx):
          
          cNvCxnSpPr = self._element.nvCxnSpPr.cNvCxnSpPr
          endCxn = cNvCxnSpPr.get_or_add_endCxn()
          endCxn.id = shape.shape_id
          endCxn.idx = cxn_pt_idx
docs: Add or update an endCxn element for this connector that connects its
          end point to the connection point of *shape* specified by
          *cxn_pt_idx*.