> gem -v
0.9.0

> gemri String
/usr/lib/ruby/1.8/rdoc/ri/ri_descriptions.rb:99:in `concat': can't
convert nil into Array (TypeError)
        from /usr/lib/ruby/1.8/rdoc/ri/ri_descriptions.rb:99:in
`merge_in'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_reader.rb:56:in `get_class'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_reader.rb:52:in `get_class'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_driver.rb:70:in
`report_class_stuff'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_driver.rb:106:in
`get_info_for'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_driver.rb:135:in
`process_args'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_driver.rb:134:in
`process_args'
        from /usr/bin/gemri:24

> gemri Hoe
[snip]  OK

> ri String
[snip] OK