[0.10.0rc1] has_many doesn't work without serializer defined on association

[JustinAiken]

I have this serializer:

class BrandSerializer < ActiveModel::Serializer
  attributes ...

  ...
  has_many :style_configurations
...
end

style_configurations doesn't have an AMS defined, it's just using the standard rails json response. Under 0.9x this works fine, but on today's new RC, I get this:

     NoMethodError:
       undefined method `new' for nil:NilClass
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/active_model_serializers-0.10.0.rc1/lib/active_model/serializer/array_serializer.rb:17:in `block in initialize'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/relation/delegation.rb:46:in `map'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.1/lib/active_record/relation/delegation.rb:46:in `map'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/active_model_serializers-0.10.0.rc1/lib/active_model/serializer/array_serializer.rb:12:in `initialize'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/active_model_serializers-0.10.0.rc1/lib/active_model/serializer.rb:215:in `new'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/active_model_serializers-0.10.0.rc1/lib/active_model/serializer.rb:215:in `block in each_association'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/active_model_serializers-0.10.0.rc1/lib/active_model/serializer.rb:208:in `each'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/active_model_serializers-0.10.0.rc1/lib/active_model/serializer.rb:208:in `each_association'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/active_model_serializers-0.10.0.rc1/lib/active_model/serializer/adapter/json.rb:17:in `serializable_hash'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/active_model_serializers-0.10.0.rc1/lib/active_model/serializer/adapter.rb:23:in `as_json'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/activesupport-4.2.1/lib/active_support/json/encoding.rb:34:in `encode'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/activesupport-4.2.1/lib/active_support/json/encoding.rb:21:in `encode'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/activesupport-4.2.1/lib/active_support/core_ext/object/json.rb:37:in `to_json_with_active_support_encoder'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/actionpack-4.2.1/lib/action_controller/metal/renderers.rb:116:in `block in <module:Renderers>'
     # /Users/jaiken/.rvm/gems/ruby-2.2.1/gems/active_model_serializers-0.10.0.rc1/lib/action_controller/serialization.rb:49:in `block (2 levels) in <module:Serialization>'

[CV-Gate]

Same here, I avoided that error specifying a serializer for the relationship.

[bf4]

Duplicate of #870

[JustinAiken]

I think it's similar symptoms, but not a dup of #870...

• Problem with each_serializer: foo and has_many associations #870 deals more with when the serializer for the has_many does exist, but the options hash for getting the association isn't passing through okay..
• This one is for when the child serializer doesn't exist at all. In previous versions of AMS, if you have a Foo model and a Bar model, and the FooSerializer has_many :bars, but there's no BarSerializer at all, it would just stick the standard rails build-in serialization to populate the the bars field... now it tosses up that error.

[joaomdmoura]

I'm also not sure if it's a dup. Not sure if #949 impacts it.
Would be awesome to have a PR with a falling test on this one 😄 @JustinAiken would you be able to do this?

[bf4]

I think this is related to #945 (comment) as well

[JustinAiken]

Would be awesome to have a PR with a falling test on this one 😄 @JustinAiken would you be able to do this?

Done in #955

[joaomdmoura]

Yeah it's definitely related to #945, I'm interested in make this happen!
@JustinAiken made a great work writing the falling test, I'll try to pick up from there, but I'm kind busy with other couple features now, so in case some of you want to implement it just make yourself comfortable and let me know, otherwise I'll work on it once I finished this new PR, what might be this weekend 😄