运行以下命令时，我得到以下堆栈跟踪：
dart generate.dart package -input googleapis-discovery-documents/ -output googleapis/
我下载的App Engine API发现文档位于当前目录中的googleapis-discovery-documents /中。
NoSuchMethodError: method not found: 'toLowerCase'
Receiver: null
Arguments: []
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:45)
#1 ApisPackageGenerator.generateApiPackage (package:discoveryapis_generator/src/apis_package_generator.dart:70:49)
#2 generateApiPackage (package:discoveryapis_generator/discoveryapis_generator.dart:53:49)
#3 generateAllLibraries (package:discoveryapis_generator/discoveryapis_generator.dart:64:28)
#4 main (file:///home/tom/work/dart/dart-sdk/discovery_api_dart_client_generator/bin/generate.dart:112:40)
#5 _startIsolate (dart:isolate-patch/isolate_patch.dart:237)
#6 _startMainIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:192)
#7 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:130)**