fix: Unhandled exception Null check operator used on a null value

[zacksleo]

fixed #151

flutter 3.7 没有 flutterVersion 输出

flutter --version --machine 
{
  "frameworkVersion": "3.7.12",
  "channel": "stable",
  "repositoryUrl": "https://github.com/flutter/flutter.git",
  "frameworkRevision": "4d9e56e694b656610ab87fcf2efbcd226e0ed8cf",
  "frameworkCommitDate": "2023-04-17 21:47:46 -0400",
  "engineRevision": "1a65d409c7a1438a34d21b60bf30a6fd5db59314",
  "dartSdkVersion": "2.19.6",
  "devToolsVersion": "2.20.1",
  "flutterRoot": "/Users/zacksleo/flutter"
}

[lijy91]

@all-contributors please add @zacksleo for code

[allcontributors]

@lijy91

I've put up a pull request to add @zacksleo! 🎉