Selecting a single column from a Nullable child Entity queries the whole object

[IvanJosipovic]

Steps to reproduce

http://pastebin.com/mXCLp8du

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;
using Microsoft.EntityFrameworkCore;

namespace EFBug
{
    public class Program
    {
        public static void Main(string[] args)
        {
            using (var db = new TestContext())
            {
                db.Parent.Add(new Parent { Child = new Child() {ChildData = "Childtest"} });
                var count = db.SaveChanges();

                string data1 = db.Parent.Select(x => x.Child.ChildData).First();

                //Query is
                //SELECT TOP(1) [x.Child].[ChildData]
                //FROM [Parent] AS[x]
                //INNER JOIN [Child] AS[x.Child] ON[x].[ChildId] = [x.Child].[Id]


                string data2 = db.Parent.Select(x => x.NullableChild.ChildData).First();

                //Query is 
                //SELECT [x].[Id], [x].[ChildId], [x].[NullableChildId], [x.NullableChild].[Id], [x.NullableChild].[ChildData], [x.NullableChild].[ChildData1], [x.NullableChild].[ChildData2], [x.NullableChild].[ChildData3]
                //FROM [Parent] AS[x]
                //LEFT JOIN [Child] AS[x.NullableChild] ON[x].[NullableChildId] = [x.NullableChild].[Id]
                //ORDER BY [x].[NullableChildId]

            }
        }
    }

    public class TestContext : DbContext
    {
        public DbSet<Parent> Parent { get; set; }
        public DbSet<Child> Child { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=EFBug;Trusted_Connection=True;");
        }
    }

    public class Parent
    {
        public Parent() {}

        [Key]
        public int Id { get; set; }

        [ForeignKey("NullableChild")]
        public int? NullableChildId { get; set; }
        public Child NullableChild { get; set; }

        [ForeignKey("Child")]
        public int ChildId { get; set; }
        public Child Child { get; set; }
    }

    public class Child
    {
        public Child(){}

        [Key]
        public int Id { get; set; }

        public string ChildData { get; set; }
        public string ChildData1 { get; set; }
        public string ChildData2 { get; set; }
        public string ChildData3 { get; set; }
    }
}

The issue

When selecting a single column from a Nullable child Entity, the whole Object is selected rather than a single property. See code above.

string data1 = db.Parent.Select(x => x.Child.ChildData).First();

//Query is
//SELECT TOP(1) [x.Child].[ChildData]
//FROM [Parent] AS[x]
//INNER JOIN [Child] AS[x.Child] ON[x].[ChildId] = [x.Child].[Id]


string data2 = db.Parent.Select(x => x.NullableChild.ChildData).First();

//Query is 
//SELECT [x].[Id], [x].[ChildId], [x].[NullableChildId], [x.NullableChild].[Id], [x.NullableChild].[ChildData], [x.NullableChild].[ChildData1], [x.NullableChild].[ChildData2], [x.NullableChild].[ChildData3]
//FROM [Parent] AS[x]
//LEFT JOIN [Child] AS[x.NullableChild] ON[x].[NullableChildId] = [x.NullableChild].[Id]
//ORDER BY [x].[NullableChildId]

Further technical details

EF Core version: 1.0.0
Operating system: Windows 10
Visual Studio version: (e.g. VS 2013 or n/a) Visual Studio 2015

Other details about my project setup:

[maumar]

dupe of #4588