Addressed PR comments

Author: Ross Ackland

lib/builders/response_builder.rb

@@ -52,7 +52,8 @@ def with_status_message(status_message)
       # @param transformer name [String]
       # @return [ResponseBuilder] response builder for chaining
       def with_transformer(transformer)
-        @options.key?(:transformers) ? @options[:transformers] << transformer : @options[:transformers] = [transformer]
+        @options[:transformers] ||= []
+        @options[:transformers] << transformer
         self
       end