maybeWhen<TResult extends Object?>  method 
- @optionalTypeArgs
- TResult $default(- String exchangeId,
- ExchangeAsset asset,
- String amount,
- String recipient,
 
- required TResult orElse(),
A variant of when that fallback to an orElse callback.
It is equivalent to doing:
switch (sealedClass) {
  case Subclass(:final field):
    return ...;
  case _:
    return orElse();
}
Implementation
@optionalTypeArgs TResult maybeWhen<TResult extends Object?>(TResult Function( String exchangeId,  ExchangeAsset asset,  String amount,  String recipient)?  $default,{required TResult orElse(),}) {final _that = this;
switch (_that) {
case _GetExchangeUrlParams() when $default != null:
return $default(_that.exchangeId,_that.asset,_that.amount,_that.recipient);case _:
  return orElse();
}
}