AssertionError [ERR_ASSERTION]: Task function must be specified

новичок в этом деле и не понимаю в чем ошибка, копировал с сайта browsersync

gulpfile.js:

var gulp        = require('gulp');
var browserSync = require('browser-sync').create();
var sass        = require('gulp-sass');

// Static Server + watching scss/html files
gulp.task('serve', gulp.src('sass'), function() {

    browserSync.init({
        server: "./src"
    });

    gulp.watch("src/sass/*.sass", gulp.parallel('sass'));
    gulp.watch("src/*.html").on('change', browserSync.reload);
});

// Compile sass into CSS & auto-inject into browsers
gulp.task('sass', function() {
    return gulp.src("src/sass/*.sass")
        .pipe(sass())
        .pipe(gulp.dest("src/css"))
        .pipe(browserSync.stream());
});

gulp.task('default', gulp.series('serve'));

Терминал:

AssertionError [ERR_ASSERTION]: Task function must be specified
    at Gulp.set [as _setTask] (C:\Users\lun2t\Desktop\lesson_11\node_modules\undertaker\lib\set-task.js:10:3)
    at Gulp.task (C:\Users\lun2t\Desktop\lesson_11\node_modules\undertaker\lib\task.js:13:8)
    at Object.<anonymous> (C:\Users\lun2t\Desktop\lesson_11\gulpfile.js:6:6)      
    at Module._compile (internal/modules/cjs/loader.js:1068:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1097:10)     
    at Module.load (internal/modules/cjs/loader.js:933:32)
    at Function.Module._load (internal/modules/cjs/loader.js:774:14)
    at Module.require (internal/modules/cjs/loader.js:957:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at requireOrImport (C:\Users\lun2t\AppData\Roaming\npm\node_modules\gulp\node_modules\gulp-cli\lib\shared\require-or-import.js:19:11) {
  generatedMessage: false,
  code: 'ERR_ASSERTION',
  actual: false,
  expected: true,
  operator: '=='
}