How to use the xgcm.duck_array_ops._pad_array function in xgcm

boundary_kwargs = dict(boundary=boundary, fill_value=fill_value)

        # now pad / trim the data as necessary
        # here we enumerate all the valid possible shifts
        if (pos == "center" and to == "right") or (pos == "left" and to == "center"):
            # do nothing, this is the default for how cumsum works
            data = da_cum.data
        elif (pos == "center" and to == "left") or (pos == "right" and to == "center"):
            data = _pad_array(
                da_cum.isel(**{dim: slice(0, -1)}), dim, left=True, **boundary_kwargs
            )
        elif (pos == "center" and to == "inner") or (pos == "outer" and to == "center"):
            data = da_cum.isel(**{dim: slice(0, -1)}).data
        elif (pos == "center" and to == "outer") or (pos == "inner" and to == "center"):
            data = _pad_array(da_cum, dim, left=True, **boundary_kwargs)
        else:
            raise ValueError(
                "From `%s` to `%s` is not a valid position "
                "shift for cumsum operation." % (pos, to)
            )

        da_cum_newcoord = self._wrap_and_replace_coords(da, data, to, keep_coords)
        return da_cum_newcoord

if to is None:
            to = self._default_shifts[pos]

        # first use xarray's cumsum method
        da_cum = da.cumsum(dim=dim)

        boundary_kwargs = dict(boundary=boundary, fill_value=fill_value)

        # now pad / trim the data as necessary
        # here we enumerate all the valid possible shifts
        if (pos == "center" and to == "right") or (pos == "left" and to == "center"):
            # do nothing, this is the default for how cumsum works
            data = da_cum.data
        elif (pos == "center" and to == "left") or (pos == "right" and to == "center"):
            data = _pad_array(
                da_cum.isel(**{dim: slice(0, -1)}), dim, left=True, **boundary_kwargs
            )
        elif (pos == "center" and to == "inner") or (pos == "outer" and to == "center"):
            data = da_cum.isel(**{dim: slice(0, -1)}).data
        elif (pos == "center" and to == "outer") or (pos == "inner" and to == "center"):
            data = _pad_array(da_cum, dim, left=True, **boundary_kwargs)
        else:
            raise ValueError(
                "From `%s` to `%s` is not a valid position "
                "shift for cumsum operation." % (pos, to)
            )

        da_cum_newcoord = self._wrap_and_replace_coords(da, data, to, keep_coords)
        return da_cum_newcoord