2) Mongoid::Factory.from_db when the attributes are nil when model class is an inheritance root sets the attributes to _type only
     Failure/Error: document.attributes.should == {'_type' => 'Address'}
     
       expected: {"_type"=>"Address"}
            got: {} (using ==)
       Diff:
       @@ -1,2 +1 @@
       -"_type" => "Address",
       
     # ./spec/mongoid/factory_spec.rb:224:in `block (5 levels) in <top (required)>'
     # ./spec/lite_spec_helper.rb:68:in `block (3 levels) in <top (required)>'
     # ./spec/lite_spec_helper.rb:67:in `block (2 levels) in <top (required)>'