title: Gulp: error in console, assert.js:90 throw new assert.AssertionError
body: <p>I get such an error in console:
  $ gulp</p>
  
  <pre><code>assert.js:90
    throw new assert.AssertionError({
    ^
  AssertionError: Task function must be specified
  
  at Gulp.set [as _setTask] (C:\Users\user\Projects\New project\node_modules\undertaker\lib\set-task.js:10:3)
  
  at Gulp.task (C:\Users\user\Projects\New project\node_modules\undertaker\lib\task.js:13:8)
  
  at Object.&lt;anonymous&gt; (C:\Users\user\Projects\New project\gulpfile.js:44:6)
  at Module._compile (module.js:541:32)
  at Object.Module._extensions..js (module.js:550:10)
  at Module.load (module.js:458:32)
  at tryModuleLoad (module.js:417:12)
  at Function.Module._load (module.js:409:3)
  at Module.require (module.js:468:17)
  at require (internal/module.js:20:19)
  </code></pre>
  
  <p>Here is my gulpfile:</p>
  
  <pre><code>var gulp = require('gulp');
  var build = require('gulp-build');
  var sass = require('gulp-sass');
  var sourcemaps = require('gulp-sourcemaps');
  var browser_sync = require('browser-sync');
  var gulps = require("gulp-series");
  
  
  //gulp-build
  gulp.task('build', function() {
      gulp.src('scripts/*.js')
          .pipe(build({
              GA_ID: '123456'
          }))
          .pipe(gulp.dest('dist'))
  });
  
  //gulp-sass
  gulp.task('sass', function() {
      return gulp.src('scss/**/*.scss')
          .pipe(sourcemaps.init())
          .pipe(sass({
              errLogToConsole: true,
              outputStyle: 'expanded'
          }).on('error', sass.logError))
          .pipe(sourcemaps.write('./maps'))
          .pipe(gulp.dest('css'));
  });
  
  //gulp-browser-sync
  gulp.task('browser_sync', function() {
      var files = [
          '*.html',
          'css/*.css'
      ];
      browser_sync.init(files, {
          server: {
              baseDir: './'
          }
      });
  });
  
  //gulp-watch
  gulp.task('watch', ['sass'], function() {
      gulp.watch('scss/**/*.scss', ['sass']);
  });
  
  //gulp-series
  gulps.registerTasks({
      "test1": (function(done) {
          setTimeout(function() {
              console.log("test1 is done");
              done();
          }, 1000);
      }),
      "test2": (function() {
          console.log("test2 is done");
      })
  });
  
  gulps.registerSeries("default", ["test1", "test2"]);
  
  // gulp.task('default', ['watch', 'browser_sync'], function() {});
  </code></pre>
  
  <p>I'm just a beginner, have you any idea what I've done wrong?</p>