throws stack trace with certain cloudformation errors

Here's what I found when trying to update (note: the response hash was me debugging it):

``` shell
2013-07-14 23:12:34 -0700 INFO : Updating Cloud Formation stack lc-pod-2-prod-1-elb-1.

{"xmlns"=>"http://cloudformation.amazonaws.com/doc/2010-05-15/", "Error"=>[{"Type"=>["Receiver"], "Code"=>["InternalFailure"]}], "RequestId"=>["883cacea-ed15-11e2-a33b-3f6dc9cefd86"]}

/Users/tbishop/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/simple_deploy-0.7.5/lib/simple_deploy/aws/cloud_formation/error.rb:16:in `process': undefined method `each' for nil:NilClass (NoMethodError)
```