title: force grails to treat a string parameter as collection of string
body: <p>In grails, I have a Controller that expects a 'options' parameter that is sent via POST that  can be a collection, i.e. 'options=A&amp;options=B&amp;options=C' which gets into grails, thanks to grails magic, as options = <em>Collection of String with value ['A','B','C']</em>.
  Problem is, when the user only picks one option, then the parameter becomes string and not string[] (or List) and when doing options.each then each, by groovy magic, gets processed character by character... how can I force options to be string[] or List so options.each is applied correctly?</p>