laravel-mix cannot read property '_walk' of null uglifyjs

laravel-mix 1.0
参考 https://github.com/mishoo/UglifyJS2/issues/3274

解决方案：

//node_modules\laravel-mix\src\config.js
uglify: {
            sourceMap: true,
            uglifyOptions: {
                compress: {
                    warnings: false,
                    collapse_vars: false,//添加这一行
                },
                output: {
                    comments: false
                }
            }
        },