title: Rails 5 actioncable undefined method `fetch' for nil:NilClass
body: <p>I am using Rails 5 with <code>actioncable</code> and I am getting <a href="https://gist.github.com/adham90/e385b2b5bbd6800e0b9a">this error</a> when trying send anything that throws <code>actioncable</code> What should i do?
  I'm trying to push the project to Heroku.</p>
  
  <pre><code>NoMethodError in MessagesController#create
  
  undefined method `fetch' for nil:NilClass
  Extracted source (around line #37):
  
  #35       # Also makes sure proper dependencies are required.
  #36       def pubsub_adapter
  *37         adapter = (cable.fetch('adapter') { 'redis' })
  #38         path_to_adapter = "action_cable/subscription_adapter/#{adapter}"
  #39         begin
  #40           require path_to_adapter
  
  Extracted source (around line #50):
  
  #48       # Adapter used for all streams/broadcasting.
  #49       def pubsub
  *50         @pubsub ||= config.pubsub_adapter.new(self)
  #51       end
  #52 
  #53       # All the identifiers applied to the connection class associated with this server.
  
  Extracted source (around line #42):
  
  #40           def broadcast(message)
  #41             server.logger.info "[ActionCable] Broadcasting to #{broadcasting}: #{message}"
  *42             server.pubsub.broadcast broadcasting, ActiveSupport::JSON.encode(message)
  #43           end
  #44         end
  #45     end
  
  
  Rails.root: /media/adham/Data/code/rails5test
  
  Application Trace
  app/controllers/messages_controller.rb:6:in `create'
  app/middleware/chat_action_cable.rb:10:in `call'
  </code></pre>