Resolving .js files in a gem

I am using the zurb-foundation gem and I add "//= require foundation" as below to include it in the asset pipeline. Everything works but Rubymine underlines "foundation" with an error "cannot resolve symbol 'foundation'". Any ideas how to get it to acknowledge its existence cause it does work ( as removing and re-adding the offending line shows ).
Thanks
Colin

//= require jquery
//= require jquery_ujs
//= require foundation
//= require_tree .