有没有办法解决gulp中的assert.js：385错误？

Question

我似乎无法使gulp正常工作，它不会按需编译和启动本地服务器。我尝试降级，卸载升级，但似乎没有任何效果。我想念什么吗？

错误：

assert.js:385
    throw err;
    ^

AssertionError [ERR_ASSERTION]: Task function must be specified
    at Gulp.set [as _setTask] (C:\Users\thebl\fusion\node_modules\undertaker\lib\set-task.js:10:3)
    at Gulp.task (C:\Users\thebl\fusion\node_modules\undertaker\lib\task.js:13:8)gulpfile.js:32:6)
    at Module._compile (internal/modules/cjs/loader.js:1137:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1157:10)
    at Module.load (internal/modules/cjs/loader.js:985:32)
    at Function.Module._load (internal/modules/cjs/loader.js:878:14)
    at Module.require (internal/modules/cjs/loader.js:1025:19)
    at require (internal/modules/cjs/helpers.js:72:18)
    at execute (C:\Users\thebl\AppData\Roaming\npm\node_modules\gulp-cli\lib\versioned\^4.0.0\index.js:36:18) {
  generatedMessage: false,
  code: 'ERR_ASSERTION',
  actual: false,
  expected: true,
  operator: '=='
}

代码：

'use strict';

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

gulp.task('sass', function() {
    return gulp.src('./css*.scss')
    .pipe(sass().on('error',sass.logError))
    .pipe(gulp.dest('./css'));
});

gulp.task('sass:watch', function() {
    gulp.watch('./css/*.scss', ['sass']); 
});

gulp.task('browser-sync', function() {
    var files = [
        './*.html',
        './css/*.css',
        './js/*.js',
        './img/*.{png,jpg,gif}'
    ];

    browserSync.init(files, {
        server: {
            baseDir: './'
        },
    });
});

gulp.task('default', ['browser-sync'], function() {   
    gulp.start('sass:watch');
});