serializeToMap method Null safety
Implementation
Map<String, dynamic> serializeToMap() {
// Don't write default ZERODIGIT, conserves space, but also minimize file
// churn.
var basicMap = _serializeToMap();
if (ZERODIGIT != null && ZERODIGIT != '') {
basicMap['ZERODIGIT'] = ZERODIGIT;
}
return basicMap;
}