不能在XML序列化中隐式转换类型系统泛型列表

我有一个asp.net应用程序背后的c#代码。试图使用类序列化为xml。但是得到错误:

 cannot implicitly convert Cannot convert type system.collection.generic.list

本行出现在:

 CourtDocumentEvent = new List<DocumentEventCourtDocumentEvent>

.CS文件代码:

AddOdyDocToWorkflowRequest AddOdyDocToWorkflowRequest = new AddOdyDocToWorkflowRequest()
{
    CaseDocument = new List<CaseDocument>()
    {
        new CaseDocument() 
        {
            CaseAugmentation = new List<CaseAugmentation>(){
                new CaseAugmentation(){
                    DocumentEvent = new List<DocumentEvent>()
                    {
                        new DocumentEvent()
                        {
                            CourtDocumentEvent = new List<DocumentEventCourtDocumentEvent>()
                            {
                                new DocumentEventCourtDocumentEvent()
                                {
                                    DocumentData = CaseNumberTextBox.Text+ "," + DocumentCode
                                }
                            }
                        }
                    }
                }
            }
        }
    }
};

    public static string ConvertToXml(object obj)
    {
        StringWriter result = new StringWriter(new StringBuilder());
        try
        {
            XmlSerializer serializer = new XmlSerializer(obj.GetType());
            serializer.Serialize(result, obj);
            return result.ToString();
        }
        catch (Exception ex)
        {
            return result.ToString();
        }
    }