Exception of parser for allowMultiple not handled

[zoechi]

Unhandled exception:
devserver: error: argument directories: Directory "a" not found.

0 applyUsageToCommandInvocation.parseArg (package:unscripted/src/usage.dart:328:7)

1 applyUsageToCommandInvocation..parseValue (package:unscripted/src/usage.dart:360:36)

2 MappedListIterable.elementAt (dart:_internal/iterable.dart:413)

3 UnmodifiableListView.

4 Object&ListMixin.elementAt (dart:collection/list.dart:58)

5 ListIterator.moveNext (dart:_internal/iterable.dart:341)

6 StringBuffer.writeAll (dart:core-patch/string_buffer_patch.dart:86)

7 IterableBase.iterableToFullString (dart:collection/iterable.dart:264)

8 Object&ListMixin.toString (dart:collection/list.dart:513)

9 _StringBase._interpolateSingle (dart:core-patch/string_patch.dart:804)

10 print (dart:core/print.dart:9)

11 devServerArgs (package:bwu_dev_server/bin/main.dart:26:3)

12 Function._apply (dart:core-patch/function_patch.dart:7)

13 Function.apply (dart:core-patch/function_patch.dart:28)

14 FunctionScript._getTopCommandResult (package:unscripted/src/script_impl.dart:156:67)

15 DeclarationScript._handleResults (package:unscripted/src/script_impl.dart:107:21)

16 ScriptImpl.execute.. (package:unscripted/src/script_impl.dart:49:11)

17 _RootZone.runUnary (dart:async/zone.dart:1149)

18 _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:502)

19 _Future._propagateToListeners (dart:async/future_impl.dart:585)

20 _Future._completeWithValue (dart:async/future_impl.dart:376)

21 _Future._asyncComplete. (dart:async/future_impl.dart:430)

22 _microtaskLoop (dart:async/schedule_microtask.dart:43)

23 _microtaskLoopEntry (dart:async/schedule_microtask.dart:52)

24 _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:96)

25 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:151)

Process finished with exit code 255

The doc for parser says

It should throw to indicate
/// that the argument is invalid.