我关注this guide。解压缩后，我运行flutter doctor并报错
⡿Unhandled exception:
NoSuchMethodError: The method '<' was called on null.
Receiver: null
Tried calling: <(Instance of 'Version')
完整堆栈
~/development/flutter/bin/flutter doctor -v
[✓] Flutter (Channel stable, v1.0.0, on Mac OS X 10.14.2 18C54, locale ru-RU)
• Flutter version 1.0.0 at /Users/naumov_evg/development/flutter
• Framework revision 5391447fae (6 weeks ago), 2018-11-29 19:41:26 -0800
• Engine revision 7375a0f414
• Dart version 2.1.0 (build 2.1.0-dev.9.4 f9ebf21297)
⡿Unhandled exception:
NoSuchMethodError: The method '<' was called on null.
Receiver: null
Tried calling: <(Instance of 'Version')
#0 Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:50:5)
#1 CocoaPods.evaluateCocoaPodsInstallation (package:flutter_tools/src/ios/cocoapods.dart:69:28)
<asynchronous suspension>
#2 CocoaPodsValidator.validate (package:flutter_tools/src/ios/ios_workflow.dart:231:12)
<asynchronous suspension>
#3 GroupedValidator.validate (package:flutter_tools/src/doctor.dart:304:52)
#4 _AsyncAwaitCompleter.start (dart:async/runtime/libasync_patch.dart:49:6)
#5 GroupedValidator.validate (package:flutter_tools/src/doctor.dart:301:36)
#6 Doctor.startValidatorTasks (package:flutter_tools/src/doctor.dart:111:52)
#7 Doctor.diagnose (package:flutter_tools/src/doctor.dart:184:41)
#8 _AsyncAwaitCompleter.start (dart:async/runtime/libasync_patch.dart:49:6)
#9 Doctor.diagnose (package:flutter_tools/src/doctor.dart:174:24)
#10 DoctorCommand.runCommand (package:flutter_tools/src/commands/doctor.dart:48:39)
#11 _AsyncAwaitCompleter.start (dart:async/runtime/libasync_patch.dart:49:6)
#12 DoctorCommand.runCommand (package:flutter_tools/src/commands/doctor.dart:34:42)
#13 FlutterCommand.verifyThenRunCommand (package:flutter_tools/src/runner/flutter_command.dart:401:18)
#14 _asyncThenWrapperHelper.<anonymous closure> (dart:async/runtime/libasync_patch.dart:77:64)
#15 _rootRunUnary (dart:async/zone.dart:1132:38)
#16 _CustomZone.runUnary (dart:async/zone.dart:1029:19)
#17 _FutureListener.handleValue (dart:async/future_impl.dart:129:18)
#18 Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:642:45)
#19 Future._propagateToListeners (dart:async/future_impl.dart:671:32)
#20 Future._complete (dart:async/future_impl.dart:476:7)
#21 _SyncCompleter.complete (dart:async/future_impl.dart:51:12)
#22 _AsyncAwaitCompleter.complete.<anonymous closure> (dart:async/runtime/libasync_patch.dart:33:20)
#23 _rootRun (dart:async/zone.dart:1124:13)
#24 _CustomZone.run (dart:async/zone.dart:1021:19)
#25 _CustomZone.bindCallback.<anonymous closure> (dart:async/zone.dart:947:23)
#26 _microtaskLoop (dart:async/schedule_microtask.dart:41:21)
#27 _startMicrotaskLoop (dart:async/schedule_microtask.dart:50:5)
#28 _runPendingImmediateCallback (dart:isolate/runtime/libisolate_patch.dart:115:13)
#29 _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:172:5)