I'm getting an exception thrown here when there are no CC recipients listed on the email.  

```
NoMethodError - undefined method `map' for nil:NilClass:
  /Users/smoovej/.rvm/gems/ruby-2.0.0-p247/bundler/gems/griddler-a6c35548a988/lib/griddler/adapters/mandrill_adapter.rb:39:in `recipients'
  /Users/smoovej/.rvm/gems/ruby-2.0.0-p247/bundler/gems/griddler-a6c35548a988/lib/griddler/adapters/mandrill_adapter.rb:17:in `block in normalize_params'
  /Users/smoovej/.rvm/gems/ruby-2.0.0-p247/bundler/gems/griddler-a6c35548a988/lib/griddler/adapters/mandrill_adapter.rb:14:in `normalize_params'
  /Users/smoovej/.rvm/gems/ruby-2.0.0-p247/bundler/gems/griddler-a6c35548a988/lib/griddler/adapters/mandrill_adapter.rb:10:in `normalize_params'
  /Users/smoovej/.rvm/gems/ruby-2.0.0-p247/bundler/gems/griddler-a6c35548a988/app/controllers/griddler/emails_controller.rb:12:in `normalized_params'
  /Users/smoovej/.rvm/gems/ruby-2.0.0-p247/bundler/gems/griddler-a6c35548a988/app/controllers/griddler/emails_controller.rb:3:in `create'
```
Happy to provide the mandrill payload if that's helpful.