parsing tags

I've got an app that allows users to assign multiple comma-delimited
tags to a new article.

Tags have and belong to many articles, and vice-versa.

On the controller, I'm trying to parse the tags like so:

@mytags = params[:tags].split(',')
@mytags.each {|a| @article.tags<<Tag.new(a) }

I'm getting this: "undefined method `stringify_keys!' for "hi":String".

Help?