export method
Implementation
@override
Map<String, dynamic>? export(OptionalPromotion e) => {
if (e.pieceLimits != null) 'pieceLimits': e.pieceLimits,
if (e.ranks != null) 'ranks': e.ranks,
if (!e.forced) 'forced': e.forced,
if (e.forced && e.forcedRanks != null) 'forcedRanks': e.forcedRanks,
};