In some conditions ToArray throws exception

I see two problems:

1. Index from base abstract class that not in hierarchy wasn't created in DB

2. When index doesn't exist ToArray fails

Success when

1. Add HierarchyRoot attribute on BaseEntity
2. Add IndexAttribute on TestEntity
3. Remove Indexed = false from Entity field (custom index also should be removed)

Sample:

using System;
using System.Linq;

using Xtensive.Orm;
using Xtensive.Orm.Configuration;

class Program
{
    static void Main(string[] args)
    {
        var dc = new DomainConfiguration("sqlserver://localhost/DO40-Tests");

        dc.Types.Register(typeof(BaseEntity));
        dc.Types.Register(typeof(TestEntity));
        dc.Types.Register(typeof(WithEntitySet));

        dc.UpgradeMode = DomainUpgradeMode.Recreate;
        var sessionConfiguration = new SessionConfiguration(SessionOptions.AutoActivation | SessionOptions.ServerProfile);

        using (var domain = Domain.Build(dc))
        {
            using (var session = domain.OpenSession(sessionConfiguration))
            using (session.Activate())
            using (var t = session.OpenTransaction())
            {
                var entity = new WithEntitySet { Name = "Test" };

                for (int i = 0; i < 250; i++)
                {
                    new TestEntity { Entity = entity, Name = "Test" };
                }

                t.Complete();
            }

            using (var session = domain.OpenSession(sessionConfiguration))
            using (session.Activate())
            using (var t = session.OpenTransaction())
            {
                Session.Current.Query.All<WithEntitySet>().First().List.ToArray();
            }
        }
    }
}

// [HierarchyRoot] with this - success
[Index("Entity", Clustered = true, Name = "Clustered")]
[Serializable]
public abstract class BaseEntity : Entity
{
    [Key]
    [Field(Nullable = false)]
    public Guid Id { get; private set; }

    // [Field] with this - success
    [Association(OnTargetRemove = OnRemoveAction.Cascade, OnOwnerRemove = OnRemoveAction.Clear)]
    [Field(Indexed = false)]
    public WithEntitySet Entity { get; set; }
}

// [Index("Entity", Clustered = true, Name = "Clustered")] with this - success
[HierarchyRoot]
public class TestEntity : BaseEntity
{
    [Key]
    [Field(Nullable = false)]
    public Guid Id { get; private set; }

    [Field(Nullable = false, Length = 400)]
    public string Name { get; set; }
}

[HierarchyRoot]
[Serializable]
public class WithEntitySet : Entity
{
    [Key]
    [Field(Nullable = false)]
    public Guid Id { get; private set; }

    [Field(Nullable = false, Length = 400)]
    public string Name { get; set; }

    [Field]
    [Association(PairTo = "Entity")]
    public EntitySet<TestEntity> List { get; set; }
}

Exception:

Object reference not set to an instance of an object.

at Xtensive.Orm.Rse.RecordSetHeader.CreateHeader(IndexInfo indexInfo)
at Xtensive.Orm.Rse.RecordSetHeader.GetHeader(IndexInfo indexInfo)
at Xtensive.Orm.Rse.RecordSetHeaderExtensions.GetRecordSetHeader(IndexInfo indexInfo)
at Xtensive.Orm.Rse.Providers.IndexProvider..ctor(IndexInfo index)
at Xtensive.Orm.Rse.IndexInfoExtensions.GetQuery(IndexInfo index)
at Xtensive.Orm.EntitySetBase.BuildEntitySetTypeState(Object key, EntitySetBase entitySet)
at Xtensive.Orm.EntitySetBase.<GetEntitySetTypeState>b__12(Object k)
at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
at Xtensive.Orm.EntitySetBase.GetEntitySetTypeState()
at Xtensive.Orm.EntitySetBase.EnsureCountIsLoaded()
at Xtensive.Orm.EntitySetBase.get_Count()
at Xtensive.Orm.EntitySet`1.System.Collections.Generic.ICollection<TItem>.get_Count()
at System.Linq.Buffer`1..ctor(IEnumerable`1 source)