！无法在序列化时为XML空节点添加结束标记

使用XmlSerializer序列化一个对象，要求把空节点表示成开始和结束标记对：

当前格式：<Wards /> 

期望格式：<Wards></Wards> 

网上搜了一下， C# - XmlSerializer Serialize empty variable to use both tags?的解决方法是：

    public class XmlTextWriterFull : XmlTextWriter {
        public XmlTextWriterFull(Stream stream, Encoding enc) : base(stream, enc) { }
        public XmlTextWriterFull(String str, Encoding enc) : base(str, enc) { }
        public XmlTextWriterFull(TextWriter sink) : base(sink) { }

        public override void WriteEndElement() {
            base.WriteFullEndElement();
        }        
    }

然后我这么调用：

    MemoryStream stream = new MemoryStream();
    XmlSerializer serializer = new XmlSerializer(message.GetType());
    XmlTextWriter writer = new XmlTextWriterFull(stream, Encoding.Unicode);
    
    serializer.Serialize(writer, message);
    StreamReader reader = new StreamReader(stream, Encoding.Unicode);
    stream.Position = 0;
    string xml = reader.ReadToEnd();
    stream.Close();
    writer.Close();
    reader.Close();  

可惜始终不成功。