title: Omniauth and Twitter callback gives TypeError
body: <p>I'm following this tutorial: <a href="http://railscasts.com/episodes/235-omniauth-part-1?view=asciicast" rel="nofollow">http://railscasts.com/episodes/235-omniauth-part-1?view=asciicast</a> to get multiple accounts with Omniauth and Devise to work with Rails 3.2.12. After I authenticate with Twitter, it redirects back to <code>../auth/twitter/callback</code> with the oauth token as parameters and in my <code>Authentication#create action</code> it says, </p>
  
  <pre><code>render :text =&gt; request.env["omniauth.auth"].to_yaml
  </code></pre>
  
  <p>But when the page renders, it says:</p>
  
  <pre class="lang-none prettyprint-override"><code>TypeError
  
  can't convert nil into String
  </code></pre>
  
  <p>The stack trace is:</p>
  
  <pre class="lang-none prettyprint-override"><code>omniauth-twitter (0.0.14) lib/omniauth/strategies/twitter.rb:23:in `+'
  omniauth-twitter (0.0.14) lib/omniauth/strategies/twitter.rb:23:in `block in &lt;class:Twitter&gt;'
  omniauth (1.1.3) lib/omniauth/strategy.rb:102:in `instance_eval'
  omniauth (1.1.3) lib/omniauth/strategy.rb:102:in `block in compile_stack'
  omniauth (1.1.3) lib/omniauth/strategy.rb:101:in `each'
  omniauth (1.1.3) lib/omniauth/strategy.rb:101:in `inject'
  omniauth (1.1.3) lib/omniauth/strategy.rb:101:in `compile_stack'
  (eval):7:in `info_stack'
  omniauth (1.1.3) lib/omniauth/strategy.rb:315:in `info'
  omniauth (1.1.3) lib/omniauth/strategy.rb:328:in `auth_hash'
  omniauth (1.1.3) lib/omniauth/strategy.rb:355:in `callback_phase'
  omniauth-oauth (1.0.1) lib/omniauth/strategies/oauth.rb:58:in `callback_phase'
  omniauth (1.1.3) lib/omniauth/strategy.rb:219:in `callback_call'
  omniauth (1.1.3) lib/omniauth/strategy.rb:175:in `call!'
  omniauth (1.1.3) lib/omniauth/strategy.rb:157:in `call'
  omniauth (1.1.3) lib/omniauth/builder.rb:48:in `call'
  warden (1.2.1) lib/warden/manager.rb:35:in `block in call'
  warden (1.2.1) lib/warden/manager.rb:34:in `catch'
  warden (1.2.1) lib/warden/manager.rb:34:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
  rack (1.4.5) lib/rack/etag.rb:23:in `call'
  rack (1.4.5) lib/rack/conditionalget.rb:25:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/head.rb:14:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/flash.rb:242:in `call'
  rack (1.4.5) lib/rack/session/abstract/id.rb:210:in `context'
  rack (1.4.5) lib/rack/session/abstract/id.rb:205:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/cookies.rb:341:in `call'
  activerecord (3.2.12) lib/active_record/query_cache.rb:64:in `call'
  activerecord (3.2.12) lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
  activesupport (3.2.12) lib/active_support/callbacks.rb:405:in `_run__3143814823160835356__call__2946912839493394460__callbacks'
  activesupport (3.2.12) lib/active_support/callbacks.rb:405:in `__run_callback'
  activesupport (3.2.12) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
  activesupport (3.2.12) lib/active_support/callbacks.rb:81:in `run_callbacks'
  actionpack (3.2.12) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/reloader.rb:65:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
  railties (3.2.12) lib/rails/rack/logger.rb:32:in `call_app'
  railties (3.2.12) lib/rails/rack/logger.rb:16:in `block in call'
  activesupport (3.2.12) lib/active_support/tagged_logging.rb:22:in `tagged'
  railties (3.2.12) lib/rails/rack/logger.rb:16:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/request_id.rb:22:in `call'
  rack (1.4.5) lib/rack/methodoverride.rb:21:in `call'
  rack (1.4.5) lib/rack/runtime.rb:17:in `call'
  activesupport (3.2.12) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
  rack (1.4.5) lib/rack/lock.rb:15:in `call'
  actionpack (3.2.12) lib/action_dispatch/middleware/static.rb:62:in `call'
  railties (3.2.12) lib/rails/engine.rb:479:in `call'
  railties (3.2.12) lib/rails/application.rb:223:in `call'
  rack (1.4.5) lib/rack/content_length.rb:14:in `call'
  railties (3.2.12) lib/rails/rack/log_tailer.rb:17:in `call'
  rack (1.4.5) lib/rack/handler/webrick.rb:59:in `service'
  /Users/ashley/.rvm/rubies/ruby-1.9.3-p385/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
  /Users/ashley/.rvm/rubies/ruby-1.9.3-p385/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
  /Users/ashley/.rvm/rubies/ruby-1.9.3-p385/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'
  </code></pre>
  
  <p>What can I do to fix this? I don't know where to begin or what's wrong.</p>