动态修改manifest.json，编译失败？

看到文档里面说可以动态修改manifest.json,然后写在vue.config.js里面编译h5就报错

replaceManifest('h5.router.base', '/webs/')  
fs.writeFileSync(manifestPath, Manifest, {  
  "flag": "w"  
})

错误是

[HBuilder] 18:00:18.386 manifest.json解析失败  
[HBuilder] 18:00:18.419  ERROR  TypeError: Cannot read property 'h5' of undefined  
[HBuilder] 18:00:18.452 TypeError: Cannot read property 'h5' of undefined  
[HBuilder] 18:00:18.485     at getH5Options (/Applications/HBuilderX.app/Contents/HBuilderX/plugins/uniapp-cli/node_modules/@dcloudio/uni-cli-shared/lib/manifest.js:47:26)  
[HBuilder] 18:00:18.486     at Object.<anonymous> (/Applications/HBuilderX.app/Contents/HBuilderX/plugins/uniapp-cli/node_modules/@dcloudio/vue-cli-plugin-uni/lib/h5/index.js:29:5)  
[HBuilder] 18:00:18.519     at Module._compile (internal/modules/cjs/loader.js:999:30)  
[HBuilder] 18:00:18.520     at Object.Module._extensions..js (internal/modules/cjs/loader.js:1027:10)  
[HBuilder] 18:00:18.552     at Module.load (internal/modules/cjs/loader.js:863:32)  
[HBuilder] 18:00:18.553     at Function.Module._load (internal/modules/cjs/loader.js:708:14)  
[HBuilder] 18:00:18.586     at Module.require (internal/modules/cjs/loader.js:887:19)  
[HBuilder] 18:00:18.586     at require (internal/modules/cjs/helpers.js:74:18)  
[HBuilder] 18:00:18.619     at module.exports (/Applications/HBuilderX.app/Contents/HBuilderX/plugins/uniapp-cli/node_modules/@dcloudio/vue-cli-plugin-uni/index.js:47:27)  
[HBuilder] 18:00:18.619     at /Applications/HBuilderX.app/Contents/HBuilderX/plugins/uniapp-cli/node_modules/@vue/cli-service/lib/Service.js:78:7  
[HBuilder] 18:00:18.652 项目 'fanqie-info' 发布h5失败.

请问一下怎么处理？完全按照官方文档写的，还是出错.....
https://uniapp.dcloud.io/collocation/vue-config