stack level too deep in rails 4.1.6

I am trying to upgrade spree to latest version and use rails 4.1.6.
However, when I go into admin order editing page. It gives me stack level too deep error.
I found out the problem is in admin order form javascript section.

```
        <% @order.shipments.each do |shipment| %>
            shipments.push(<%== shipment.to_json(:root => false, :include => [:inventory_units, :stock_location]) %>);
        <% end %>
```

After I remove these two lines, everything is fine.
I had searched in the whole spree backend, I didn't see any usage of the part of code.
I think it's just legacy code and can be removed safely.

Here is the error log:
```
[2014-10-19 10:31:20.705] [893fc6f0]
SystemStackError (stack level too deep):
  activerecord (4.1.6) lib/active_record/connection_adapters/abstract/connection_pool.rb:629
```