Fix NameError for 412Error on 412 without body

lib/aws/error_handler.rb

@@ -41,6 +41,7 @@ def error_code_for_empty_response(http_resp)
         400 => 'BadRequest',
         403 => 'Forbidden',
         404 => 'NotFound',
+        412 => 'PreconditionFailed',
       }[status_code] || "#{status_code}Error"
     end
 

spec/fixtures/operations/s3/412_response_head.yml

@@ -0,0 +1,10 @@
+operation: head_object
+params:
+  :bucket: 'bucket'
+  :key: 'key'
+response:
+  status_code: 412
+  body: ''
+error:
+  class: Aws::S3::Errors::PreconditionFailed
+  message: ''