template=edulp_article/article_libro error=undefined method `medium_url' for nil:NilClass trace=/usr/local/bundle/bundler/gems/frontend-gem-77d4e4199a97/lib/yavu/frontend/helpers/common.rb:225:in `image_url' /usr/local/bundle/bundler/gems/frontend-gem-77d4e4199a97/lib/yavu/frontend/helpers/common.rb:164:in `image_tag' (__TEMPLATE__):13:in `block in singleton class'