SPWeb.GetFolder盡管我的輸入是一個值，但我無法將字符串值傳遞給我string。private static void UploadEmlToSp(string sharePointSite, string sharePointDocLib, string emlFullPath, string requestNo){    using (SPSite oSite = new SPSite(sharePointSite))    {        using (SPWeb oWeb = oSite.OpenWeb())        {            if (!System.IO.File.Exists(emlFullPath))                throw new FileNotFoundException("File not found.", emlFullPath);            SPFolder myLibrary = oWeb.Folders[sharePointDocLib];            if (SPWeb.GetFolder(requestNo).Exists) <--errored            {                //Folder Exisits            }我可以知道我錯過了什么嗎？以下是錯誤消息。An object reference is required for the non-static field, method, or property SPWeb.GetFolder(string)