xdo.Attributes["Name"].Value.未将对象引用到实例？

请教一个关于XML的问题： 
我的XML是这样的 <?xml version="1.0" encoding="utf-8" ?> 
<FieldsMap> 
<Fields Name="ennm"  Caption="工程名称"/> 
<Fields Name="dscd"  Caption="行政区划代码"/> 
<Fields Name="dsnm"  Caption="行政区划名称"/> 
<Fields Name="ennmcd"  Caption="河流名称代码"  align="center"/> 
<Fields Name="aduncd"  Caption="管理单位代码"/> 
<Fields Name="adunnm"  Caption="管理单位名称"/> 
</FieldsMap> 
我在GridView CREA事件里访问XML中的节点 <FieldsMap>的子节点 
protected void GridView_RowCreated(object sender, GridViewRowEventArgs e) 
        {             if (e.Row.RowType == DataControlRowType.DataRow) 
            { 
                foreach (XmlNode xn1 in .DataQueryAdapter.DataQueryInterface.CfgXMLNode) 
                { 
                    if (xn1.Name == "FieldsMap") 
                    { 
                        foreach (XmlNode xdo in xn1.ChildNodes) 
                        { 
                            for (int i = 0; i < e.Row.Cells.Count; i++) 
                            { 
                                if (xdo.Attributes["Name"].Value.Trim() != null) 
                                { 
                                    if (((BoundField)(this.rpt.Columns[i])).HeaderText.Trim().Equals(xdo.Attributes["Name"].Value.Trim())) 
                                    {                                         //if (xdo.Attributes.GetNamedItem("width") != null) 
                                        //{ 
                                        //    this.rpt.Columns[i].HeaderStyle.Width = Unit.Pixel(int.Parse(xdo.Attributes.GetNamedItem("width").Value));                                         //} 
                                        if (xdo.Attributes.GetNamedItem("align") != null) 
                                        { 
                                            if (xdo.Attributes.GetNamedItem("align").Value.ToString().Trim() == "center") 
                                            {                                                 this.rpt.Columns[i].ItemStyle.HorizontalAlign = HorizontalAlign.Center;                                             } 
                                            if (xdo.Attributes.GetNamedItem("align").Value.ToString().Trim() == "left") 
                                            {                                                 this.rpt.Columns[i].ItemStyle.HorizontalAlign = HorizontalAlign.Left;                                             } 
                                            if (xdo.Attributes.GetNamedItem("align").Value.ToString().Trim().ToLower().Equals("123")) 
                                            {                                                 this.rpt.Columns[i].ItemStyle.HorizontalAlign = HorizontalAlign.Right;                                             } 
                                        } 
                                    } 
                                } 
                            }                         } 
                    } 
                }             } 
        }
但是总报错说xdo.Attributes["Name"].Value.未将对象引用到实例？为什么啊，各位哥们