'Return the line spacing value calculated from the combination of
*spacing_line* and *spacing_lineRule*. Returns a |float| number of
lines when *spacing_lineRule* is ``WD_LINE_SPACING.MULTIPLE``,
otherwise a |Length| object of absolute line height is returned.
Returns |None| when *spacing_line* is |None|.'

@staticmethod
def _line_spacing(spacing_line, spacing_lineRule):

    if (spacing_line is None):
        return None
    if (spacing_lineRule == WD_LINE_SPACING.MULTIPLE):
        return (spacing_line / Pt(12))
    return spacing_line
