SumAsync throw Exception when used over float?

[iyhammad]

SumAsync is throwing
System.InvalidOperationException: No coercion operator is defined between types 'System.Threading.Tasks.Task`1[System.Single]' and 'System.Nullable`1[System.Single]'.
when using it over an owned type. when used with float? after upgrading from EFCore 2.0 to 2.1

Exception Details

No coercion operator is defined between types 'System.Threading.Tasks.Task`1[System.Single]' and 'System.Nullable`1[System.Single]'.
System.InvalidOperationException: No coercion operator is defined between types 'System.Threading.Tasks.Task`1[System.Single]' and 'System.Nullable`1[System.Single]'.
   at System.Linq.Expressions.Expression.GetUserDefinedCoercionOrThrow(ExpressionType coercionType, Expression expression, Type convertToType)
   at System.Linq.Expressions.Expression.Convert(Expression expression, Type type, MethodInfo method)
   at Microsoft.EntityFrameworkCore.Query.Internal.RelationalResultOperatorHandler.HandleSum(HandlerContext handlerContext)
   at Microsoft.EntityFrameworkCore.Query.Internal.RelationalResultOperatorHandler.HandleResultOperator(EntityQueryModelVisitor entityQueryModelVisitor, ResultOperatorBase resultOperator, QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitResultOperator(ResultOperatorBase resultOperator, QueryModel queryModel, Int32 index)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitResultOperator(ResultOperatorBase resultOperator, QueryModel queryModel, Int32 index)
   at Remotion.Linq.Clauses.ResultOperatorBase.Accept(IQueryModelVisitor visitor, QueryModel queryModel, Int32 index)
   at Remotion.Linq.QueryModelVisitorBase.VisitResultOperators(ObservableCollection`1 resultOperators, QueryModel queryModel)
   at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateAsyncQueryExecutor[TResult](QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileAsyncQuery[TResult](QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileAsyncQueryCore[TResult](Expression query, IQueryModelGenerator queryModelGenerator, IDatabase database)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass22_0`1.<CompileAsyncQuery>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddAsyncQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileAsyncQuery[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.ExecuteAsync[TResult](Expression expression, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.SumAsync(IQueryable`1 source, CancellationToken cancellationToken)
   at HRPayroll.Leave.Data.EntityFramework.Repositories.LeaveRequestRepository.<GetLeavesSumAsync>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 Abp.Threading.InternalAsyncHelper.<AwaitTaskWithPostActionAndFinallyAndGetResult>d__5`1.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.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
   at HrPayroll.Leave.Core.LeaveBalance.LeaveBalanceService.<GetEmployeeLeaveConsumptionAsync>d__10.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.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
   at HrPayroll.Leave.Core.LeaveBalance.LeaveBalanceService.<GetEmployeeLeaveBalanceToDateAsync>d__9.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.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
   at HrPayroll.Leave.Application.LeaveBalances.LeaveBalanceApplicationService.<GetEmployeeLeavesBalancesToDate>d__8.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 lambda_method(Closure , Object )
   at Microsoft.Extensions.Internal.ObjectMethodExecutorAwaitable.Awaiter.GetResult()
   at Microsoft.AspNetCore.Mvc.Internal.ActionMethodExecutor.AwaitableObjectResultExecutor.<Execute>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 Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeActionMethodAsync>d__12.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 Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeNextActionFilterAsync>d__10.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Rethrow(ActionExecutedContext context)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeInnerFilterAsync>d__13.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 Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.<InvokeNextExceptionFilterAsync>d__24.MoveNext()

Steps to reproduce

1. Define an owned entity with float? property
2. Define and an owner entity
3. Call SumAsyn using the Owner Set to sum the owned entity field.
   below the same owner & owned entities and the exception happens only with the SumAsync

##LeaveRequestRepository .cs

 var sumLeavsFullyPaid =
                this.Context.Set<LeaveRequest>()
                    .Where(predicate).Select(z => z.TakenBalance.FullyPaid).Sum(); // success
            var sumPartiallyPaid = await
                this.Context.Set<LeaveRequest>()
                    .Where(predicate).Select(z => z.TakenBalance.PartiallyPaid).SumAsync().ConfigureAwait(false); //throw exception

Further technical details

EF Core version: 2.1.0
Database Provider: Microsoft.EntityFrameworkCore.SqlServer
Operating system: Windows 10 Enterprise, Build: 17134.48
IDE: Visual Studio 2017 15.7.3

[maumar]

regression introduced in 4bb6c38 - in order to produce 0 for sum of empty collections we strip the nullability and then try to cast the result back to nullable. This doesn't work for async because Task, hence the exception.