Update grandchild, where child is linktable

[Jogai]

I'm trying to update a graph where the child is just for linking to the grandchild, however the child is inserted with only NULL values leaving the grandchild unlinked. How can I solve this?

My code

                _db.UpdateGraph(sector, up => up
                    .OwnedEntity(s => s.Image, date => date
                        .OwnedEntity(i => i.Picture))
                    );

Executed SQL:

SET SESSION sql_mode='ANSI';INSERT INTO `Images`(
`PictureId`, 
`PhotoId`) VALUES (
NULL, 
NULL);
SELECT
`Id`
FROM `Images`
WHERE  row_count() > 0 AND `Id`=last_insert_id();
SET SESSION sql_mode='ANSI';INSERT INTO `Pictures`(
`Logo`, 
`Path`, 
`Description`, 
`Created`) VALUES (
0, 
'/User_Data/Misc/2016/5/12/Untitled.gif' /* @gp1 */, 
NULL, 
5/12/2016 9:05:13 AM /* @gp2 */);
SELECT
`Id`
FROM `Pictures`
WHERE  row_count() > 0 AND `Id`=last_insert_id()

My models:

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

        public string Name { get; set; }

        public bool Active { get; set; }

        public int? ImageId { get; set; }

        public virtual Image Image { get; set; }
    }

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

        public int? PictureId { get; set; }

        public Picture Picture { get; set; }

        public int? PhotoId { get; set; }

        public Photo Photo { get; set; }

        public virtual ICollection<Sector> Sectors { get; set; }
    }

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

        public string Path { get; set; }

        public string Description { get; set; }

        public DateTime Created { get; set; }
    }

Code first configuration:

    public class ImageEntityConfig : EntityTypeConfiguration<Image>
    {
        public ImageEntityConfig()
        {
            HasOptional(i => i.Picture)
                .WithMany()
                .HasForeignKey(i => i.PictureId);
            HasOptional(i => i.Photo)
                .WithMany()
                .HasForeignKey(i => i.PhotoId);
        }
    }