undefined method `bytesize' for Hash

[alfo]

When calling ip.authenticate, from the example, using faraday 0.8.7, faraday_middleware 0.9.0:

ip.authenticate 'me@alexforey.com', 'password'
NoMethodError: undefined method `bytesize' for #<Hash:0x007f8943602768>
        from /Users/alexforey/.rvm/rubies/ruby-1.9.3-p374/lib/ruby/1.9.1/net/http.rb:1932:in `send_request_with_body'
        from /Users/alexforey/.rvm/rubies/ruby-1.9.3-p374/lib/ruby/1.9.1/net/http.rb:1919:in `exec'
        from /Users/alexforey/.rvm/rubies/ruby-1.9.3-p374/lib/ruby/1.9.1/net/http.rb:1317:in `block in transport_request'
        from /Users/alexforey/.rvm/rubies/ruby-1.9.3-p374/lib/ruby/1.9.1/net/http.rb:1316:in `catch'
        from /Users/alexforey/.rvm/rubies/ruby-1.9.3-p374/lib/ruby/1.9.1/net/http.rb:1316:in `transport_request'
        from /Users/alexforey/.rvm/rubies/ruby-1.9.3-p374/lib/ruby/1.9.1/net/http.rb:1293:in `request'
        from /Users/alexforey/.rvm/rubies/ruby-1.9.3-p374/lib/ruby/1.9.1/net/http.rb:1286:in `block in request'
        from /Users/alexforey/.rvm/rubies/ruby-1.9.3-p374/lib/ruby/1.9.1/net/http.rb:745:in `start'
        from /Users/alexforey/.rvm/rubies/ruby-1.9.3-p374/lib/ruby/1.9.1/net/http.rb:1284:in `request'
        from /Users/alexforey/.rvm/gems/ruby-1.9.3-p374/gems/faraday-0.8.7/lib/faraday/adapter/net_http.rb:75:in `perform_request'
        from /Users/alexforey/.rvm/gems/ruby-1.9.3-p374/gems/faraday-0.8.7/lib/faraday/adapter/net_http.rb:38:in `call'
        from /Users/alexforey/.rvm/gems/ruby-1.9.3-p374/gems/instapaper_full-0.0.4/lib/faraday/oauth.rb:17:in `call'
        from /Users/alexforey/.rvm/gems/ruby-1.9.3-p374/gems/faraday-0.8.7/lib/faraday/connection.rb:247:in `run_request'
        from /Users/alexforey/.rvm/gems/ruby-1.9.3-p374/gems/faraday-0.8.7/lib/faraday/connection.rb:112:in `post'
        from /Users/alexforey/.rvm/gems/ruby-1.9.3-p374/gems/instapaper_full-0.0.4/lib/instapaper_full.rb:41:in `authenticate'
        from (irb):2
        from /Users/alexforey/.rvm/gems/ruby-1.9.3-p374/gems/railties-3.2.9/lib/rails/commands/console.rb:47:in `start'
        from /Users/alexforey/.rvm/gems/ruby-1.9.3-p374/gems/railties-3.2.9/lib/rails/commands/console.rb:8:in `start'
        from /Users/alexforey/.rvm/gems/ruby-1.9.3-p374/gems/railties-3.2.9/lib/rails/commands.rb:41:in `<top (required)>'
        from script/rails:6:in `require'
        from script/rails:6:in `<main>'1.9.3-p374 :003 >