gruntjs – 引用Grunt对象导致Warning：Object true没有方法’indexOf’

'use Strict';
module.exports = function(grunt) {

    // Project configuration.
    grunt.initConfig({
        pkg: grunt.file.readJSON('package.json'),//Define paths
        js_src_path:    'webapp/js',js_build_path:  'webapp/js',css_src_path:   'webapp/css',css_build_path: 'webapp/css',less_src_path:  'webapp/less',less_build_path:'webapp/less',//Convert Less to CSS and minify if compress = true
        less: {
            development: {
                options: {
                    path: ['<%= less_src_path %>'],},files: {
                    //'<%= less_build_path %>/app.css':'<%= concat.less.dest %>',//Dynamic expansion 1:1 
                    expand: true,cwd:    '<%= less_src_path %>',dest:   '<%= less_build_path %>',src:    '*.less',ext:    '.less.css'
                }
            },production: {
                options: {
                    path: ['<%= less_src_path %>'],//compress: true 
                    yuicompress: true
                },ext:    '.less.min.css'
                }
            }
        }
    });

    // Load the plugin that provides the tasks.
    grunt.loadNpmTasks('grunt-lib-contrib');
    grunt.loadNpmTasks('grunt-contrib-less');

    // Task(s).
    grunt.registerTask('les',['less']);
    grunt.registerTask('proless',['less:production']);
    grunt.registerTask('devless',['less:devevelopment']);
};

运行下列各项：

grunt les
grunt proless
grunt devless

结果是：

Warning: Object true has no method 'indexOf' Use --force to conTinue

如果我删除任务开发：{…}和’production：{….}’并离开内部，只需更改我的帐号，以减少它的工作正常。