copy method
Implementation
IsoMsg copy() {
final IsoMsg out = IsoMsg()
..isoHeader = isoHeader
..trailer = trailer
..rejectCode = rejectCode
..captureTime = captureTime
..responseTime = responseTime;
fields.forEach((int field, IsoComponent<Object> component) {
out.fields[field] = component is IsoMsg ? component.copy() : component;
});
out.markDirty();
return out;
}