* ActiveMerchant depends upon ActiveSupport, which provides us with String#blank? and String#present? among other things, which are a shorter ways of checking for nil or an empty string (or not).
* Let's see if we can improve the "no error message" error message a bit, it might help anyone in future trying to diagnose an issue. I had a quick look at a few other gateways for guidance on what's typically accepted.

I would suggest:

```ruby
if response['returnText'].present?
  response['returnText']
else
  "Invalid response received from the CommerceGate API. Please contact CommerceGate support if you continue to receive this message. (The raw response returned by the API was #{response.inspect})"
end
```