AAA syntax:ReturnRecursiveFakes not faking private members

    public class AnObject
    {
        public void DoNothing()
        {

        }
    }

    public class AnWrapperObject
    {
        private AnObject objAn;
        public void CallDoNothing()
        {
            objAn.DoNothing();
        }
    }

    [TestFixture]
    public class TestClass
    {
        public void Test1()
        {
            AnWrapperObject wrappObj = Isolate.Fake.Instance<AnWrapperObject>(Members.ReturnRecursiveFakes);
            Isolate.WhenCalled(() => wrappObj.CallDoNothing()).CallOriginal();
            wrappObj.CallDoNothing();
        }
    }

TestCase 'TestClass.Test1' failed: Object reference not set to an instance of an object.
   System.NullReferenceException: Object reference not set to an instance of an object.

private AnObject objAn;

public AnObject objAn
{
get;
private set;
}