title: Throws Assertion error
body: <p>Searching via same question couldn't solve.
  I am working on the bootstrap 4 installation with the help of this guy's <a href="https://coursetro.com/posts/code/130/Learn-Bootstrap-4-Final-in-2018-with-our-Free-Crash-Course" rel="nofollow noreferrer">https://coursetro.com/posts/code/130/Learn-Bootstrap-4-Final-in-2018-with-our-Free-Crash-Course</a>  tutorial.  </p>
  
  <p>When followed the same: I see</p>
  
  <p>Gulp: error in console, assert.js:90 throw new assert.AssertionError</p>
  
  <pre><code> AssertionError [ERR_ASSERTION]: Task function must be specified
      at Gulp.set [as _setTask] (C:\Users\dc\Projects\main-pro
  ject\bs4\node_modules\undertaker\lib\set-task.js:10:3)
      at Gulp.task (C:\Users\dc\Projects\main-project\bs4\node
  _modules\undertaker\lib\task.js:13:8)
      at Object.&lt;anonymous&gt; (C:\Users\dc\Projects\main-project
  \bs4\gulpfile.js:21:6)
      at Module._compile (module.js:652:30)
      at Object.Module._extensions..js (module.js:663:10)
      at Module.load (module.js:565:32)
      at tryModuleLoad (module.js:505:12)
      at Function.Module._load (module.js:497:3)
      at Module.require (module.js:596:17)
      at require (internal/module.js:11:18)
  </code></pre>
  
  <p>and this is my gulpfile.js</p>
  
  <pre><code>    var gulp        = require('gulp');
  var browserSync = require('browser-sync').create();
  var sass        = require('gulp-sass');
  
  // Compile sass into CSS &amp; auto-inject into browsers
  gulp.task('sass', function() {
      return gulp.src(['node_modules/bootstrap/scss/bootstrap.scss', 'src/scss/*.scss'])
          .pipe(sass())
          .pipe(gulp.dest("src/css"))
          .pipe(browserSync.stream());
  });
  
  // Move the javascript files into our /src/js folder
  gulp.task('js', function() {
      return gulp.src(['node_modules/bootstrap/dist/js/bootstrap.min.js', 'node_modules/jquery/dist/jquery.min.js', 'node_modules/popper.js/dist/umd/popper.min.js'])
          .pipe(gulp.dest("src/js"))
          .pipe(browserSync.stream());
  });
  
  // Static Server + watching scss/html files
  gulp.task('serve', ['sass'], function() {
  
      browserSync.init({
          server: "./src"
      });
  
      gulp.watch(['node_modules/bootstrap/scss/bootstrap.scss', 'src/scss/*.scss'], ['sass']);
      gulp.watch("src/*.html").on('change', browserSync.reload);
  });
  
  gulp.task('default', ['js','serve']);
  </code></pre>