A null value was returned where an instance of httpresponsemessage was expected.

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C#

Ajax

JSON

WebAPI

I am executing the following code to get data from Web API:

$(window).load(function () {
           var jsonObject = {
               "CompanyID": 1,
               "UserName": '30',
               "UserPwd": '30',
               "UserRole": 3,
               "RemoteHostIP": '8.8.8.8'
           };
           //debugger;
           $.ajax({
               type: "POST"
                , url: "http://localhost/ESSWebAPI/api/mobi/Login_User",
               data: JSON.stringify(jsonObject),
               contentType: "application/json;charset=utf-8",
               dataType: "json"
                        , success: function (data) {
                            console.log(data);
                        },
               error: function (response) {
                   alert(response.status + " " + response.statusText);
               }
           });
       });

I am getting the following error:

A null value was returned where an instance of HttpResponseMessage was expected.

System.InvalidOperationException

at System.Web.Http.Controllers.ResponseMessageResultConverter.Convert(HttpControllerContext controllerContext, Object actionResult) at System.Web.Http.Controllers.ApiControllerActionInvoker.<invokeactionasynccore>d__0.MoveNext()--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Controllers.ActionFilterResult.<executeasync>d__2.MoveNext()--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Dispatcher.HttpControllerDispatcher.<sendasync>d__1.MoveNext()

at System.Web.Http.Controllers.ResponseMessageResultConverter.Convert(HttpControllerContext controllerContext, Object actionResult) at System.Web.Http.Controllers.ApiControllerActionInvoker.<invokeactionasynccore>d__0.MoveNext()--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Controllers.ActionFilterResult.<executeasync>d__2.MoveNext()--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.Dispatcher.HttpControllerDispatcher.<sendasync>d__1.MoveNext()


Code in my Web API

[HttpPost]
       //[Route("api/Mobi/Login_User")]
       public HttpResponseMessage Login_User(Login obj)
       {
           try
           {
               tlbset.ESS.Login oLogin = new tlbset.ESS.Login();
               oLogin.UserName = obj.UserName;
               oLogin.UserPwd = obj.UserPwd;
               oLogin.CompanyID = obj.CompanyID;
               oLogin.UserRole = Convert.ToInt16(obj.UserRole);
               oLogin.RemoteHostIP = obj.RemoteHostIP;
               //RemoteHostName
               try
               {
                   System.Net.IPHostEntry host = default(System.Net.IPHostEntry);
                   host = System.Net.Dns.GetHostEntry(oLogin.RemoteHostIP);
                   oLogin.RemoteHostName = host.HostName;
               }
               catch
               {
               }

               List<Result> lstLogin = new List<Result>();

               DataSet dsResult = new DataSet("dsResult");
               DataTable dtLogin = new DataTable("dtLogin");
               DataTable dtMenu = new DataTable("dtMenu");

               dsResult.Tables.Add(dtLogin);
               dsResult.Tables.Add(dtMenu);

               if (oLogin.LoginUser())
               {
                   if (oLogin.EmpCngPwd == 0)
                   {
                       //VALID EMPLOYEE
                       dtLogin.Rows.Add(1, CT.Cryptography.Crypto.Encryption(oLogin.SessionID.ToString()));
                   }
                   else if (oLogin.EmpCngPwd == 1)
                   {
                       //PASSWORD EXPIRE
                       dtLogin.Rows.Add(3, "Your Password is expired");
                   }
                   else if (oLogin.EmpCngPwd == 2)
                   {
                       //CHANGE PASSWORD ON LOG ON
                       dtLogin.Rows.Add(3, "You must set password");
                   }
               }
               else
               {
                   //INVALID EMPLOYEE
                   dtLogin.Rows.Add(2, oLogin.ErrorMsg);
               }

               //MENU
               dtMenu = Get_Menu_Table();
               DataView dv;
               if (!oLogin.objEmployee.ReportingHead)
               {
                   //Pending Approvals
                   dv = dtMenu.DefaultView;
                   dv.RowFilter = "SNo<7 AND SNo>7.3";
                   dtMenu = dv.ToTable();

                   //Team Leave calendar
                   dv = dtMenu.DefaultView;
                   dv.RowFilter = "SNo<>9";
                   dtMenu = dv.ToTable();
               }

               //Employee Directory
               if (!oLogin.objSettings.ShowEmpDir)
               {
                   dv = dtMenu.DefaultView;
                   dv.RowFilter = "SNo<>10";
                   dtMenu = dv.ToTable();
               }

               //Web Punch
               if(!(oLogin.objSettings.ApplyMobilePunch && oLogin.objSettings.InclInMobilePunch))
               {
                   dv = dtMenu.DefaultView;
                   dv.RowFilter = "SNo<>11";
                   dtMenu = dv.ToTable();
               }

               //Payroll
               string sEmpPRModules = "";
               tlbset.ESS.Settings oSettings = new tlbset.ESS.Settings();
               if (oSettings.GetRecord())
                   sEmpPRModules = oSettings.EmpPRModules;
               if (sEmpPRModules != "")
               {//Salary Details
                   if (sEmpPRModules.Contains("1^1|") == false)
                   {
                       dv = dtMenu.DefaultView;
                       dv.RowFilter = "SNo<>8.1";
                       dtMenu = dv.ToTable();
                   }

                   //Salary register
                   if (sEmpPRModules.Contains("3^1|") == false)
                   {
                       dv = dtMenu.DefaultView;
                       dv.RowFilter = "SNo<>8.2";
                       dtMenu = dv.ToTable();
                   }

                   //if none of them is applicable
                   if (!sEmpPRModules.Contains("1^1|") && !sEmpPRModules.Contains("3^1|"))
                   {
                       dv = dtMenu.DefaultView;
                       dv.RowFilter = "SNo<8 AND SNo>8.2";
                       dtMenu = dv.ToTable();
                   }
               }
               return Request.CreateResponse(HttpStatusCode.OK, dsResult);
           }
           catch (Exception ex)
           {
               CTException.WriteDBLog(strCodeFile, "Login_User", ex.Message, ex.InnerException);
               return null;
           }
       }

What I have tried:

I have tried changing post method to GEt. But it doesnt work