add check before N+1 notification publish to prevent poly association…

… with nil type to be include

lib/jit_preloader/active_record/associations/singular_association.rb

@@ -25,7 +25,7 @@ def load_target
         end
       end
     end
-    
+
     private def not_a_polymorphic_association_with_missing_type
       !(self.is_a?(ActiveRecord::Associations::BelongsToPolymorphicAssociation) && self.klass.nil?)
     end