rails/rails — pull request #6176 by nashby (2012-05-05 17:40:23+00:00)
Title: check checkboxes with array of strings as :checked option

common use-case when you are passing `params` as `:checked` option:

```ruby
:checked => params[:contact_ids]
```
in this case params[:contact_ids] is an array of strings so you should convert it with `to_i` if you want this work.