when<TResult extends Object?>  method 
- @optionalTypeArgs
- TResult $default(- PaymentElementFieldRequired? applePay,
- PaymentElementFieldRequired? googlePay
 
A switch-like method, using callbacks.
As opposed to map, this offers destructuring.
It is equivalent to doing:
switch (sealedClass) {
  case Subclass(:final field):
    return ...;
  case Subclass2(:final field2):
    return ...;
}
Implementation
@optionalTypeArgs TResult when<TResult extends Object?>(TResult Function( PaymentElementFieldRequired? applePay,  PaymentElementFieldRequired? googlePay)  $default,) {final _that = this;
switch (_that) {
case _PaymentElementWalletOptions():
return $default(_that.applePay,_that.googlePay);case _:
  throw StateError('Unexpected subclass');
}
}