rails-api/active_model_serializers

#### Expected behavior vs actual behavior



#### Steps to reproduce
*(e.g., detailed walkthrough, runnable script, example application)*



#### Environment

ActiveModelSerializers Version *(commit ref if not on tag)*: 

Output of `ruby -e "puts RUBY_DESCRIPTION"`: 

OS Type & Version: 

Integrated application and version *(e.g., Rails, Grape, etc)*: 


#### Backtrace
*(e.g., provide any applicable backtraces from your application)*



#### Additonal helpful information
*(e.g., Gemfile.lock, configurations, PR containing a failing test, git bisect results)*