RuntimeError: Neutered Exception ActionView::Template::Error: uninitialized constant Mime::CSS

RuntimeError: Neutered Exception ActionView::Template::Error: uninitialized constant Mime::CSS
    lib/auto_complete/auto_complete_macros_helper.rb:116:in `auto_complete_stylesheet'
    lib/auto_complete/auto_complete_macros_helper.rb:108:in `text_field_with_auto_complete'
    app/helpers/application_helper.rb:166:in `texto'

Hay que cambiar MIME::CSS por MIME[:css]

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