Trying to reproduce https://github.com/ztoben/assets-webpack-plugin/issues/92

app.js

module.exports = "Exported";

gulpfile.js

const gulp = require('gulp');
const webpack = require('webpack');
const webpackStream = require('webpack-stream');
const webpackConfig = require('./webpack.config');

gulp.task('default', () => {
  return gulp.src('./app.js')
    .pipe(webpackStream(webpackConfig, webpack))
    .pipe(gulp.dest('dist/'));
});

package.json

{
  "name": "assets-webpack-bug",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "assets-webpack-plugin": "3.8.4-alpha.0",
    "gulp": "4.0.0",
    "webpack": "4.12.0",
    "webpack-cli": "3.0.6",
    "webpack-merge": "4.1.3",
    "webpack-stream": "4.0.3"
  }
}

webpack.config.js

module.exports = {
  mode: "development"
}

@Kronuz The webpack configuration is missing the assets plugin:

const AssetsPlugin = require('assets-webpack-plugin');
// ...
plugins: [
  new AssetsPlugin(),
]

I can reproduce the error running ./node_modules/.bin/gulp on Node.js version 8.11.3.