def get_empty_dtype_and_na(join_units):
    """
    Return dtype and N/A values to use when concatenating specified units.

    Returned N/A value may be None which means there was no casting involved.

    Returns
    -------
    dtype
    na
    """
    if len(join_units) == 1:
        blk = join_units[0].block
        if blk is None:
            return np.float64, np.nan

    if is_uniform_reindex(join_units):
        # XXX: integrate property
        empty_dtype = join_units[0].block.dtype
        upcasted_na = join_units[0].block.fill_value
        return empty_dtype, upcasted_na

    has_none_blocks = False
    dtypes = [None] * len(join_units)
    for i, unit in enumerate(join_units):
        if unit.block is None:
            has_none_blocks = True
        else:
            dtypes[i] = unit.dtype

    upcast_classes = defaultdict(list)
    null_upcast_classes = defaultdict(list)
    for dtype, unit in zip(dtypes, join_units):
        if dtype is None:
            continue

        if is_categorical_dtype(dtype):
            upcast_cls = 'category'
        elif is_datetime64tz_dtype(dtype):
            upcast_cls = 'datetimetz'
        elif issubclass(dtype.type, np.bool_):
            upcast_cls = 'bool'
        elif issubclass(dtype.type, np.object_):
            upcast_cls = 'object'
        elif is_datetime64_dtype(dtype):
            upcast_cls = 'datetime'
        elif is_timedelta64_dtype(dtype):
            upcast_cls = 'timedelta'
        elif is_sparse(dtype):
            upcast_cls = dtype.subtype.name
        elif is_extension_array_dtype(dtype):
            upcast_cls = 'object'
        elif is_float_dtype(dtype) or is_numeric_dtype(dtype):
            upcast_cls = dtype.name
        else:
            upcast_cls = 'float'

        # Null blocks should not influence upcast class selection, unless there
        # are only null blocks, when same upcasting rules must be applied to
        # null upcast classes.
        if unit.is_na:
            null_upcast_classes[upcast_cls].append(dtype)
        else:
            upcast_classes[upcast_cls].append(dtype)

    if not upcast_classes:
        upcast_classes = null_upcast_classes

    # create the result
    if 'object' in upcast_classes:
        return np.dtype(np.object_), np.nan
    elif 'bool' in upcast_classes:
        if has_none_blocks:
            return np.dtype(np.object_), np.nan
        else:
            return np.dtype(np.bool_), None
    elif 'category' in upcast_classes:
        return np.dtype(np.object_), np.nan
    elif 'datetimetz' in upcast_classes:
        # GH-25014. We use NaT instead of iNaT, since this eventually
        # ends up in DatetimeArray.take, which does not allow iNaT.
        dtype = upcast_classes['datetimetz']
        return dtype[0], tslibs.NaT
    elif 'datetime' in upcast_classes:
        return np.dtype('M8[ns]'), tslibs.iNaT
    elif 'timedelta' in upcast_classes:
        return np.dtype('m8[ns]'), tslibs.iNaT
    else:  # pragma
        try:
            g = np.find_common_type(upcast_classes, [])
        except TypeError:
            # At least one is an ExtensionArray
            return np.dtype(np.object_), np.nan
        else:
            if is_float_dtype(g):
                return g, g.type(np.nan)
            elif is_numeric_dtype(g):
                if has_none_blocks:
                    return np.float64, np.nan
                else:
                    return g, None

    msg = "invalid dtype determination in get_concat_dtype"
    raise AssertionError(msg)
Return dtype and N/A values to use when concatenating specified units.

    Returned N/A value may be None which means there was no casting involved.

    Returns
    -------
    dtype
    na