NullReferenceException when accessing property of an optional navigation in child projection

[imb590]

The following query fails with NullReferenceException. The exception is thrown only on async call; sync version works.

class Program
{
    static void Main(string[] args)
    {
        using (var db = new Context())
        {
            db.Database.EnsureDeleted();
            db.Database.EnsureCreated();

            db.Main.Add(new Main());
            db.SaveChanges();

            var result = db
                .Main
                .Select(m => new
                {
                    Items = m.Dependent != null
                        ? m.Dependent.Items.Select(i => new { m.Dependent.Data }).ToList()
                        : null,
                })
                .FirstOrDefaultAsync()
                .GetAwaiter()
                .GetResult();
        }
    }
}

public class Context : DbContext
{
    public DbSet<Main> Main { get; set; }
}

public class Main
{
    public int Id { get; set; }

    public OptionalDependent Dependent { get; set; }
}

public class OptionalDependent
{
    [Key]
    public int MainId { get; set; }

    public Main Main { get; set; }

    public bool Data { get; set; }

    public ICollection<Item> Items { get; set; }
}

public class Item
{
    public int Id { get; set; }

    public int OptionalDependentId { get; set; }

    public OptionalDependent OptionalDependent { get; set; }
}

Exception message: System.NullReferenceException: Object reference not set to an instance of an object.
Stack trace:
   at lambda_method(Closure )
   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal.TaskLiftingExpressionVisitor._ExecuteAsync[T](IReadOnlyList`1 taskFactories, Func`2 selector)
   at Microsoft.EntityFrameworkCore.Query.Internal.AsyncLinqOperatorProvider.AsyncSelectEnumerable`2.AsyncSelectEnumerator.MoveNext(CancellationToken cancellationToken)
   at System.Linq.AsyncEnumerable.FirstOrDefault_[TSource](IAsyncEnumerable`1 source, CancellationToken cancellationToken) in D:\a\1\s\Ix.NET\Source\System.Interactive.Async\First.cs:line 144
   at Microsoft.EntityFrameworkCore.Query.Internal.AsyncLinqOperatorProvider.TaskResultAsyncEnumerable`1.Enumerator.MoveNext(CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Query.Internal.AsyncLinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.MoveNext(CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteSingletonAsyncQuery[TResult](QueryContext queryContext, Func`2 compiledQuery, IDiagnosticsLogger`1 logger, Type contextType)
   at Program.Main(String[] args)

EF Core version: 2.2.4