I want to update a field 'End Time' of type DateTime in my Sharepoint list. I want to update the field('End Time') with null.Whenever I try this I get an exception "Input string is not in correct format". beloq is my code:

  public static void DeleteEndTime(string resource, string digest, Cookie cookie)
            var client = new RestClient();
            client.BaseUrl = new Uri(_baseUri);
            var request = new RestRequest();
            request.AddParameter(cookie.Name, cookie.Value, ParameterType.Cookie);
            request.AddHeader("Accept", "application/json");
            request.AddHeader("Content-Type", "application/json;odata=verbose");
            request.AddHeader("X-RequestDigest", digest);
            request.AddHeader("X-HTTP-Method", "MERGE");
            request.AddHeader("IF-MATCH", "*");
            request.Resource = resource;
            request.RequestFormat = DataFormat.Json;
            request.Method = Method.POST;
            string jsonbody = @"{ '__metadata':{ 'type':'SP.Data.TimesheetListItem'},'End_x0020_Time':'"+ (DateTime?)null +"'}";
            request.AddParameter("Application/Json;odata=verbose", jsonbody, ParameterType.RequestBody);
            IRestResponse response = client.Execute(request);

        catch (Exception ex)
            //TODO - Log

1 Answer 1


Your request body should be like following.

string jsonbody = @"{ '__metadata':{ 'type':'SP.Data.TimesheetListItem'},'End_x0020_Time':null}"

So try it.

'End_x0020_Time':'"+ (DateTime?)null +"' is not valid. For null values, casting is not required.

  • Was about to answer that you don't have to cast the null to Datetime :)
    – Gintas K
    Nov 3, 2016 at 12:21
  • I'm getting the following exception when I try this "Cannot convert a primitive value to the expected type 'Edm.DateTime'. See the inner exception for more details" @Atish Dipongkor
    – Dharma Raj
    Nov 3, 2016 at 12:36
  • you saved my time, But I dont understand the difference string jsonbody = @"{ '__metadata':{ 'type':'SP.Data.TimesheetListItem'},'End_x0020_Time':null} and @"{ '__metadata':{ 'type':'SP.Data.TimesheetListItem'},'End_x0020_Time':'"+ null +"'}";
    – Dharma Raj
    Nov 3, 2016 at 12:45

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