jnigen crashes on empty string in jnigen.yaml classes: section

[brianquinlan]

e.g.

classes:
  - "okhttp3.Request"
  -

dart run jnigen --config jnigen.yaml
Unhandled exception:
type 'Null' is not a subtype of type 'String' in type cast
#0      _CastListBase.[] (dart:_internal/cast.dart:99:46)
#1      ListBase.elementAt (dart:collection/list.dart:43:33)
#2      ListIterator.moveNext (dart:_internal/iterable.dart:354:26)
#3      new Config (package:jnigen/src/config/config_types.dart:284:29)
#4      Config.parseArgs (package:jnigen/src/config/config_types.dart:515:20)
#5      main (file:///Users/bquinlan/.pub-cache/hosted/pub.dev/jnigen-0.12.2/bin/jnigen.dart:12:21)
#6      _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:295:33)
#7      _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:184:12)

Not a huge deal but it took me a while to figure out that the exception was related to the missing class name.