Viewset list when using polymorphic models

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I have been trying to get the support for polymorphic model serialization to work in my latest project. When I request a specific object from my endpoint, the correct serializer is clearly instantiated and I receive the output that I would expect. When I try and retrieve a list of model instances, however, the following exception is raised:

Request Method: GET
Request URL: http://localhost:8000/projects
Django Version: 1.11
Exception Type: AttributeError
Exception Value: 'list' object has no attribute '_meta'
Exception Location: django-rest-framework-json-api/rest_framework_json_api/serializers.py in get_polymorphic_serializer_for_instance, line 279

I have tried running the example project, provided in the repo, and I'm able to reproduce the error I have been seeing.

Looking in the documentation, it is not clear whether there is currently support for serializing multiple model instances in a viewset list output. Looking at the tests for the project, I also do not see a test for this scenario.

Is this something that should be supported?

[mblayman]

Is this fixed by #402 being merged?

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Just checked and the master branch now works great! Many thanks for merging the changes!