Error: Cannot read property 'semver' of null

This is due using an emulator with an unstable Developer Preview API version. 

You probably have a device using API 27 (Android 8.1). 

Open your AVD, remove that device and re-run.

It's also useful to use --target <emulator_name> when launching the emulator if you have more than one. 

To get a list of available names to use, call the emulate command with --list

결론 :  에뮬레이터 생성시 타겟을 8.1버전으로 생성했다

하위 API레벨로 변경한다.