CalDavSynchronizer.DataAccess.CalDavDataAccess.GetVersions C# (CSharp) Method

    private async Task<IReadOnlyList<EntityVersion<WebResourceName, string>>> GetVersions (DateTimeRange? range, string entityType)
    {
      var entities = new List<EntityVersion<WebResourceName, string>>();

      try
      {
        var responseXml = await _webDavClient.ExecuteWebDavRequestAndReadResponse (
            _serverUrl,
            "REPORT",
            1,
            null,
            null,
            "application/xml",
            string.Format (
                @"<?xml version=""1.0""?>
                    <C:calendar-query xmlns:C=""urn:ietf:params:xml:ns:caldav"">
                        <D:prop xmlns:D=""DAV:"">
                            <D:getetag/>
                        </D:prop>
                        <C:filter>
                            <C:comp-filter name=""VCALENDAR"">
                                <C:comp-filter name=""{0}"">
                                  {1}
                                </C:comp-filter>
                            </C:comp-filter>
                        </C:filter>
                    </C:calendar-query>
                    ",
                entityType,
                range == null ? string.Empty : string.Format (@"<C:time-range start=""{0}"" end=""{1}""/>",
                    range.Value.From.ToString (s_calDavDateTimeFormatString),
                    range.Value.To.ToString (s_calDavDateTimeFormatString))
                ));


        XmlNodeList responseNodes = responseXml.XmlDocument.SelectNodes ("/D:multistatus/D:response", responseXml.XmlNamespaceManager);

        // ReSharper disable once LoopCanBeConvertedToQuery
        // ReSharper disable once PossibleNullReferenceException
        foreach (XmlElement responseElement in responseNodes)
        {
          var urlNode = responseElement.SelectSingleNode ("D:href", responseXml.XmlNamespaceManager);
          var etagNode = responseElement.SelectSingleNode ("D:propstat/D:prop/D:getetag", responseXml.XmlNamespaceManager);
          if (urlNode != null &&
              etagNode != null &&
              _serverUrl.AbsolutePath != UriHelper.DecodeUrlString (urlNode.InnerText))
          {
            var uri = new WebResourceName (urlNode.InnerText);
            entities.Add (EntityVersion.Create (uri, HttpUtility.GetQuotedEtag (etagNode.InnerText)));
          }
        }
      }
      catch (WebDavClientException x)
      {
        // Workaround for Synology NAS, which returns 404 insteaod of an empty response if no events are present
        if (x.StatusCode == HttpStatusCode.NotFound && await IsResourceCalender())
          return entities;

        throw;
      }

      return entities;
    }