Javascript Alpaca表单：上载字段错误：SyntaxError:JSON.parse:JSON数据第1行第1列的数据意外结束

我用羊驼为node.js站点制作了一个表单。此表单包含一个上载字段，用户选择该字段后，该字段会立即将文件发送到Mongo数据库（以及“上载”文件夹）。 文件已正确发送，但每个文件都会显示一条错误消息：

错误：SyntaxError:JSON.parse:第1行的数据意外结束 JSON数据的第1列

此处为羊驼代码（仅上传字段部分）：

和布局。jade：

doctype html
html
    head
        title= title
        meta(charset='utf-8')
        src='bower_components/jquery/dist/jquery.min.js')
        script(type='text/javascript', src='bower_components/alpaca/dist/lib/jquery/dist/jquery.js')

        script(type='text/javascript', src='//cdnjs.cloudflare.com/ajax/libs/handlebars.js/1.3.0/handlebars.min.js')
        link(rel='stylesheet', type='text/css', href='//maxcdn.bootstrapcdn.com/bootstrap/3.3.1/css/bootstrap.min.css')
        script(type='text/javascript', src='//maxcdn.bootstrapcdn.com/bootstrap/3.3.1/js/bootstrap.min.js')
        link(href='stylesheets/style.css', rel='stylesheet')
        // alpaca
        link(rel='stylesheet', type='text/css', href='bower_components/alpaca/dist/alpaca/bootstrap/alpaca.min.css' )
        script(type='text/javascript', src='bower_components/alpaca/dist/alpaca/bootstrap/alpaca.js')
        link(rel='stylesheet', type='text/css', href='bower_components/alpaca/dist/lib/jquery-file-upload/css/jquery.fileupload.css')
        link(rel='stylesheet', type='text/css', href='bower_components/alpaca/dist/lib/jquery-file-upload/css/jquery.fileupload-ui.css')
        script(src='bower_components/alpaca/dist/lib/jquery-file-upload/js/vendor/jquery.ui.widget.js')
        script(src='bower_components/alpaca/dist/lib/jquery-file-upload/js/jquery.iframe-transport.js')
        script(src='bower_components/jquery-file-upload/js/jquery.fileupload.js')
        script(src='bower_components/alpaca/dist/lib/jquery-file-upload/js/jquery.fileupload-process.js')
        script(src='bower_components/alpaca/dist/lib/jquery-file-upload/js/jquery.fileupload-ui.js')

    body
        block content
        block content2

谢谢你，对不起我的英语，我是法国人

doctype html
html
    head
        title= title
        meta(charset='utf-8')
        src='bower_components/jquery/dist/jquery.min.js')
        script(type='text/javascript', src='bower_components/alpaca/dist/lib/jquery/dist/jquery.js')

        script(type='text/javascript', src='//cdnjs.cloudflare.com/ajax/libs/handlebars.js/1.3.0/handlebars.min.js')
        link(rel='stylesheet', type='text/css', href='//maxcdn.bootstrapcdn.com/bootstrap/3.3.1/css/bootstrap.min.css')
        script(type='text/javascript', src='//maxcdn.bootstrapcdn.com/bootstrap/3.3.1/js/bootstrap.min.js')
        link(href='stylesheets/style.css', rel='stylesheet')
        // alpaca
        link(rel='stylesheet', type='text/css', href='bower_components/alpaca/dist/alpaca/bootstrap/alpaca.min.css' )
        script(type='text/javascript', src='bower_components/alpaca/dist/alpaca/bootstrap/alpaca.js')
        link(rel='stylesheet', type='text/css', href='bower_components/alpaca/dist/lib/jquery-file-upload/css/jquery.fileupload.css')
        link(rel='stylesheet', type='text/css', href='bower_components/alpaca/dist/lib/jquery-file-upload/css/jquery.fileupload-ui.css')
        script(src='bower_components/alpaca/dist/lib/jquery-file-upload/js/vendor/jquery.ui.widget.js')
        script(src='bower_components/alpaca/dist/lib/jquery-file-upload/js/jquery.iframe-transport.js')
        script(src='bower_components/jquery-file-upload/js/jquery.fileupload.js')
        script(src='bower_components/alpaca/dist/lib/jquery-file-upload/js/jquery.fileupload-process.js')
        script(src='bower_components/alpaca/dist/lib/jquery-file-upload/js/jquery.fileupload-ui.js')

    body
        block content
        block content2