ArgumentError: Unknow url

UrlExpander::Client.expand("https://t.co/J6JNYgLs")
ArgumentError: Unknow url
    from /Users/tomo/.rvm/gems/ruby-1.9.3-p125/gems/url_expander-0.1.5/lib/url_expander.rb:42:in `expand'
    from (irb):4
    from /Users/tomo/.rvm/rubies/ruby-1.9.3-p125/bin/irb:16:in`<main>'
