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*.

def _connect_end_to(self, shape, cxn_pt_idx):
        """
        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*.
        """
        cNvCxnSpPr = self._element.nvCxnSpPr.cNvCxnSpPr
        endCxn = cNvCxnSpPr.get_or_add_endCxn()
        endCxn.id = shape.shape_id
        endCxn.idx = cxn_pt_idx