Fix problem with tests in jruby 1.7.13

By https://github.com/railsware/js-routes/pull/123 pull request
But in 1.7.13 we can test this with `nil`:

```ruby
expect(evaljs("window.jQuery.param(#{_value.to_json.inspect})")).to eq(_value.to_param)
```

So test case will check anyway.