System.NullReferenceException on navigational property (2.0)

This query:

var resultWorks = await this.context.Carts
                .Where(t => t.OwnerId == this.LoggedInUserId)
                .Select(t => new
                {
                    something = t.Configuration != null && t.Configuration.Parameters != null ? t.Configuration.Parameters.ToArray() : null
                })
                .ToArrayAsync();

Entity framework class:

//Partial DbCart:
        public int? ConfigurationId { get; set; }
        public DbConfiguration Configuration { get; set; }

//Partial DbConfiguration 
public List<DbConfigurationParameter> Parameters { get; set; }

throws error

Exception message: System.NullReferenceException: 'Object reference not set to an instance of an object.'
Stack trace:
Microsoft.EntityFrameworkCore.Query.Internal.IncludeCompiler+<_IncludeAsync>d__18.MoveNext()
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
System.Runtime.CompilerServices.TaskAwaiter.GetResult()
Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal.TaskLiftingExpressionVisitor+<_ExecuteAsync>d__8.MoveNext()
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor+AsyncSelectEnumerable+AsyncSelectEnumerator+<MoveNext>d__3.MoveNext()
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
System.Runtime.CompilerServices.TaskAwaiter.GetResult()
Microsoft.EntityFrameworkCore.Query.Internal.AsyncLinqOperatorProvider+ExceptionInterceptor+EnumeratorExceptionInterceptor+<MoveNext>d__5.MoveNext()
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
System.Runtime.CompilerServices.ConfiguredTaskAwaitable+ConfiguredTaskAwaiter.GetResult()
System.Collections.Generic.AsyncEnumerableHelpers+<ToArrayWithLength>d__1.MoveNext()
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
System.Runtime.CompilerServices.ConfiguredTaskAwaitable+ConfiguredTaskAwaiter.GetResult()
System.Collections.Generic.AsyncEnumerableHelpers+<ToArray>d__0.MoveNext()
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
System.Runtime.CompilerServices.TaskAwaiter.GetResult()

Further technical details

EF Core version: (2.0) Database Provider: (Microsoft.EntityFrameworkCore.SqlServer) - SQL Server 2016 Operating system: Windows 10 IDE: (e.g. Visual Studio 2017)

Query is part of bigger query, which freeze entire execution of code. Step over (F10) never actually step over and web request nevery finish executing (there is no response to client, no error nothing). This worked with EF Core 1.1.2.

return await this.context.Carts
                .Where(t => t.OwnerId == this.LoggedInUserId)
                .OrderBy(t => t.Order).ThenBy(t => t.Id)
                .Select(t => new ViewCartModel()
                {
                    id = t.Id,
                    quantity = t.Quantity,
                    model = t.Title,
                    modelId = t.ModelId,
                    configurationId = t.ConfigurationId,
                    processing = false,
                    price = t.Configuration.Parameters
                        .Where(t2 => t2.Parameter.PriceType == ePriceType.Price)
                        .Select(t2 => BitConverter.ToDouble(t2.ParameterValue.Value, 0))
                        .Sum()
                })
                .ToArrayAsync();

[ivanovmv90]

Looks like problem with async methods. For me, problem dissapeared after changing ToListAsync() with ToList().

Also, https://github.com/aspnet/EntityFrameworkCore/issues/9449

[ajcvickers]

@MaklaCof Thanks for the feedback; much appreciated.