ExtJs4.2，文件上传，无法提交至指定URL

ExtJs4.2，文件上传，无法提交至指定URL。用浏览器调试JS，发现总报如下的错：
Uncaught NotFoundError: Failed to execute 'appendChild' on 'Node': The new child element is null.  
我的JS代码如下：

				items : [ {
					xtype : 'textfield',
					inputType : 'file',
					///id : ...
				} ]

继续用浏览器调试跟踪：

//ext-all-dev.js:124759L
  isFileUpload: function() {
        return this.inputType === 'file'; //返回true
    },

//ext-all-dev.js:121545L
        // Special handling for file upload fields: since browser security measures prevent setting
        // their values programatically, and prevent carrying their selected values over when cloning,
        // we have to move the actual field instances out of their components and into the form.
        len = uploadFields.length;


        for (i = 0; i < len; ++i) {
            el = uploadFields[i].extractFileInput(); //返回null
            formEl.appendChild(el); //报错：Uncaught NotFoundError
            uploadEls.push(el);
        }
        
//ext-all-dev.js:123915L
    extractFileInput: function() {
        return null;
    },        
    

经查，发现filefield的extractFileInput返回的不是null，所以，试着将上述的代码修改为：

				items : [ {
					xtype : 'filefield',
					///id : ...
				} ]

问题解决！