Cannot read property 'hash' of undefined

[xiaomaer]

使用 "speed-measure-webpack-plugin": "1.3.1"时，html-webpack-plugin升级到“4.0.0-beta.5”，打包报错；去掉 "speed-measure-webpack-plugin"打包正常。详细参考：
stephencookdev/speed-measure-webpack-plugin#57

[PLQin]

see mzgoddard/hard-source-webpack-plugin#416

It might solve your problem