post<M>  method 
Implementation
void post<M>({
  M Function(TransitionContext ctx, D data)? getValue,
  M? value,
  String? label,
}) {
  _handler = _postWithContext<M, D>(
    (transCtx) => transCtx.dataValueOrThrow<D>(),
    getValue,
    value,
    label,
  );
}