Self Serve mode: Exception is encountered during saving the beneficiary details

Company: Wheaton Franciscan Healthcare For Load Testing
Environment: Us Azure (https://azure.workterra.net)

Scenario: Self Serve mode

Steps:
1. Login as a employee
2. Traverse below pages:
a. Agreement Acceptance
b. Demographics
3. Add Spouse
4. Add Child
5. Wave the Medical Plan
6. From Dental -> Base Select spouse and Child and Save
7. From Vision -> Vision Exam PLus -> Select Spouse and child and do Enroll now
8. from Supp AD&D -> Employee Supplemental AD&D -> Select value from drop down -> Enroll Now
9. from STD Buy Up -> STD 20% Buy Up (matched with Plan 1) -> Select value from drop down -> Enroll Now
10. Voluntary LTD -> LTD 20% buy Up -> Select value from drop down -> Enroll Now
11. From Legal -> 2017 Legal -> Select Spouse and child and do Enroll now
12. Form DCRA -> Dependent Daycare -> Enter Value in and Enroll Now
13. Continue
14. From Beneficiaries Page -> Add the Beneficiary for below:
a. 'Basic Life - Regular or Religious or Seasonal Worker or Academic - Basic Life' and Save
b. Basic AD&D - Regular or Religious or Seasonal Worker or Academic - Basic AD&D-> Save
c. Employee Supplemental AD&D - Supp AD&D -> Save

15. Click on Continue
16. success message for Beneficiary is displayed

Actual Result:
Error message is displayed as 'Server Encountered and internal error. Please contact your administrator.'

also below exception is displayed:

Exception : Value cannot be null.Parameter name: source
App Error Log : -
Employee ID : 255
Action Name : EmployeeBeneficiary
Model : System.Web.Mvc.HandleErrorInfo
Controller : UserDetails
Web Error Log : at System.Linq.Enumerable.Where[TSource](IEnumerable`1 source, Func`2 predicate)
at WORKTERRA.BenAdmin.Areas.UserDetails.Models.EmployeeBeneficiaryModel.ValidatePlanBeneficiary()
at WORKTERRA.BenAdmin.Areas.UserDetails.Controllers.UserDetailsController.EmployeeBeneficiary(EmployeeBeneficiaryModel objEmployeeBeneficiaryModel)
at lambda_method(Closure , ControllerBase , Object[] )
at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)
at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.ActionInvocation.InvokeSynchronousActionMethod()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.b__39(IAsyncResult asyncResult, ActionInvocation innerInvokeState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`2.CallEndDelegate(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase`1.End()
at System.Web.Mvc.Async.AsyncResultWrapper.End[TResult](IAsyncResult asyncResult, Object tag)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.b__3d()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c_DisplayClass46.b_3f()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c_DisplayClass46.b_3f()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c_DisplayClass33.b_32(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.CallEndDelegate(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase`1.End()
at System.Web.Mvc.Async.AsyncResultWrapper.End[TResult](IAsyncResult asyncResult, Object tag)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c_DisplayClass21.<>cDisplayClass2b.b_1c()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c_DisplayClass21.b_1e(IAsyncResult asyncResult)