system.Data.Entity.Infrastructure.DbUpdateConcurrencyException: Store update, insert, or delete statement affected an unexpected number of rows (). Entities may have been modified or deleted since entities were loaded. See http://go.microsoft.com/fwlink/?LinkId=472540 for information on understanding and handling optimistic concurrency exceptions. ---> System.Data.Entity.Core.OptimisticConcurrencyException: Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. See http://go.microsoft.com/fwlink/?LinkId=472540 for information on understanding and handling optimistic concurrency exceptions.

   at System.Data.Entity.Core.Mapping.Update.Internal.UpdateTranslator.ValidateRowsAffected(Int64 rowsAffected, UpdateCommand source)

   at System.Data.Entity.Core.Mapping.Update.Internal.UpdateTranslator.Update()

   at System.Data.Entity.Core.EntityClient.Internal.EntityAdapter.<Update>b__2(UpdateTranslator ut)

   at System.Data.Entity.Core.EntityClient.Internal.EntityAdapter.Update[T](T noChangesResult, Func` updateFunction)

   at System.Data.Entity.Core.EntityClient.Internal.EntityAdapter.Update()

   at System.Data.Entity.Core.Objects.ObjectContext.<SaveChangesToStore>b__35()

   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func` func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)

   at System.Data.Entity.Core.Objects.ObjectContext.SaveChangesToStore(SaveOptions options, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction)

   at System.Data.Entity.Core.Objects.ObjectContext.<>c__DisplayClass2a.<SaveChangesInternal>b__27()

   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func` operation)

   at System.Data.Entity.Core.Objects.ObjectContext.SaveChangesInternal(SaveOptions options, Boolean executeInExistingTransaction)

   at System.Data.Entity.Core.Objects.ObjectContext.SaveChanges(SaveOptions options)

   at System.Data.Entity.Internal.InternalContext.SaveChanges()

   --- End of inner exception stack trace ---

   at System.Data.Entity.Internal.InternalContext.SaveChanges()

   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()

   at Repository.Pattern.Ef6.DataContext.SaveChanges()

   at Repository.Pattern.Ef6.UnitOfWork.SaveChanges()

   at NISWebSet.Web.Api.Billing_InvoicingDetailApiController.<ReturnBilling>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.Threading.Tasks.TaskHelpersExtensions.<CastToObject>d__3`.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.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.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>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.Controllers.AuthenticationFilterResult.<ExecuteAsync>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.ExceptionFilterResult.<ExecuteAsync>d__0.MoveNext()