c# - コード分​​析は、オブジェクトが複数回破棄される可能性があることを訴えています。なんで？

Question

responseStream次の関数で警告が表示されます。

private static string GetResponseString(WebResponse response)
        {
            using (var responseStream = response.GetResponseStream())
            {
                if (responseStream != null)
                {
                    using (var responseReader = new StreamReader(responseStream))
                    {
                        var strResponse = responseReader.ReadToEnd();
                        return strResponse;
                    }
                }
            }

            return string.Empty;
        }

この関数は、次のような場所から呼び出します。

var request = (HttpWebRequest)WebRequest.Create(Uri);
            request.Headers.Add("Authorization", "GoogleLogin auth=" + this.SecurityToken);
            request.ContentType = "application/x-www-form-urlencoded";
            request.Method = "POST";
            request.Timeout = 5000;

            // build the post string     
            var postString = new StringBuilder();
            postString.AppendFormat("registration_id={0}", recipientId);
            postString.AppendFormat("&data.payload={0}", message);
            postString.AppendFormat("&collapse_key={0}", collapseKey);

            // write the post-string as a byte array     
            var requestData = Encoding.ASCII.GetBytes(postString.ToString());
            request.ContentLength = requestData.Length;
            var requestStream = request.GetRequestStream();
            requestStream.Write(requestData, 0, requestData.Length);
            requestStream.Close();

            // Do the actual request and read the response stream  
            try
            {
                var response = request.GetResponse();
                var responseString = GetResponseString(response);
                response.Close();

                return responseString.Contains("id=") 
                    ? SendStatus.Ok 
                    : GetSendStatusFromResponse(responseString);
            }
            catch (WebException ex)
            {
                var webResponse = (HttpWebResponse)ex.Response;
                if (webResponse != null)
                {
                    if (webResponse.StatusCode.Equals(HttpStatusCode.Unauthorized))
                    {
                        return SendStatus.Unauthorized;
                    }

                    if (webResponse.StatusCode.Equals(HttpStatusCode.ServiceUnavailable))
                    {
                        return SendStatus.ServiceUnavailable;
                    }
                }

                this.LoggerService.Log(null, ex);
                return SendStatus.GeneralException;
            }