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##### SUMMARY
When testing ansible-test sanity with a collection, I see the following traceback, at first I thought it was because of a missing file, but adding it doesn't fix the issue.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
ansible-test

##### ANSIBLE VERSION
923e21836b1a4fb91aa6e93463efe0aea4022144 Move plugin loader playbook dir additions back to Playbook instead of PlaybookCLI (#59557)

##### CONFIGURATION
https://logs.zuul.ansible.com/34/34/89748bcccaba051183f1e8819502c7398b4d2206/check/ansible-test-sanity/c8e84e5/zuul-info/inventory.yaml

##### OS / ENVIRONMENT
fedora 29 from zuul.ansible.com


##### STEPS TO REPRODUCE
Run ansible-test with the following: 

source ~/venv/bin/activate; /home/zuul/src/github.com/ansible/ansible/bin/ansible-test sanity -vv --requirements --python 3.6 --lint

from
 /home/zuul/src/github.com/ansible-network/sandbox/ansible_collections/ansible_network/sandbox

example logs: https://logs.zuul.ansible.com/34/34/89748bcccaba051183f1e8819502c7398b4d2206/check/ansible-test-sanity/c8e84e5/ara-report/result/7b2fad99-9bc4-41bc-a264-b71819b0d659/

##### EXPECTED RESULTS
ansible-test to pass

##### ACTUAL RESULTS
https://logs.zuul.ansible.com/34/34/89748bcccaba051183f1e8819502c7398b4d2206/check/ansible-test-sanity/c8e84e5/job-output.html#l1031
```
2019-08-06 21:13:50.017154 | fedora-29 | Traceback (most recent call last):
2019-08-06 21:13:50.017311 | fedora-29 |   File "/home/zuul/src/github.com/ansible/ansible/bin/ansible-test", line 15, in <module>
2019-08-06 21:13:50.017361 | fedora-29 |     lib.cli.main()
2019-08-06 21:13:50.017454 | fedora-29 |   File "/home/zuul/src/github.com/ansible/ansible/test/runner/lib/cli.py", line 125, in main
2019-08-06 21:13:50.017540 | fedora-29 |     args.func(config)
2019-08-06 21:13:50.017686 | fedora-29 |   File "/home/zuul/src/github.com/ansible/ansible/test/runner/lib/sanity/__init__.py", line 156, in command_sanity
2019-08-06 21:13:50.017748 | fedora-29 |     settings = test.load_processor(args)
2019-08-06 21:13:50.017853 | fedora-29 |   File "/home/zuul/src/github.com/ansible/ansible/test/runner/lib/sanity/__init__.py", line 803, in load_processor
2019-08-06 21:13:50.017911 | fedora-29 |     return SanityIgnoreProcessor(args, self, None)
2019-08-06 21:13:50.018011 | fedora-29 |   File "/home/zuul/src/github.com/ansible/ansible/test/runner/lib/sanity/__init__.py", line 448, in __init__
2019-08-06 21:13:50.018089 | fedora-29 |     self.parser = SanityIgnoreParser.load(args)
2019-08-06 21:13:50.018193 | fedora-29 |   File "/home/zuul/src/github.com/ansible/ansible/test/runner/lib/sanity/__init__.py", line 426, in load
2019-08-06 21:13:50.018290 | fedora-29 |     SanityIgnoreParser.instance = SanityIgnoreParser(args)
2019-08-06 21:13:50.018450 | fedora-29 |   File "/home/zuul/src/github.com/ansible/ansible/test/runner/lib/sanity/__init__.py", line 278, in __init__
2019-08-06 21:13:50.018574 | fedora-29 |     paths_by_test[test.name] = set(target.path for target in test.filter_targets(test_targets))
2019-08-06 21:13:50.018711 | fedora-29 |   File "/home/zuul/src/github.com/ansible/ansible/test/runner/lib/sanity/import.py", line 62, in filter_targets
2019-08-06 21:13:50.018806 | fedora-29 |     return [target for target in targets if os.path.splitext(target.path)[1] == '.py' and
2019-08-06 21:13:50.018908 | fedora-29 |   File "/home/zuul/src/github.com/ansible/ansible/test/runner/lib/sanity/import.py", line 63, in <listcomp>
2019-08-06 21:13:50.019077 | fedora-29 |     (is_subdir(target.path, data_context().content.module_path) or is_subdir(target.path, data_context().content.module_utils_path))]
2019-08-06 21:13:50.019178 | fedora-29 |   File "/home/zuul/src/github.com/ansible/ansible/test/runner/lib/util.py", line 782, in is_subdir
2019-08-06 21:13:50.019225 | fedora-29 |     if not path.endswith(os.sep):
2019-08-06 21:13:50.019291 | fedora-29 | AttributeError: 'NoneType' object has no attribute 'endswith'
```

"""Create a Layout using the given root and paths."""
        plugin_types = sorted(set(p.split('/')[1] for p in paths if re.search(r'^plugins/[^/]+/', p)))
        provider_types = sorted(set(p.split('/')[2] for p in paths if re.search(r'^test/provider/[^/]+/', p)))
        plugin_paths = dict((p, os.path.join('plugins', p)) for p in plugin_types)
        provider_paths = dict((p, os.path.join('test/provider', p)) for p in provider_types)
        collection_root = os.path.dirname(os.path.dirname(root))
        collection_dir = os.path.relpath(root, collection_root)
        collection_namespace, collection_name = collection_dir.split(os.sep)
        collection_prefix = '%s.%s.' % (collection_namespace, collection_name)
        collection_root = os.path.dirname(collection_root)
        return ContentLayout(root,
                             paths,
                             plugin_paths=plugin_paths,
                             provider_paths=provider_paths,
                             code_path='',
                             collection=CollectionDetail(
                                 name=collection_name,
                                 namespace=collection_namespace,
                                 root=collection_root,
                                 prefix=collection_prefix,
                             ),
                             util_path='test/util',
                             unit_path='test/unit',
                             unit_module_path='test/unit/plugins/modules',
                             unit_module_utils_path='test/unit/plugins/module_utils',
                             integration_path='test/integration',
                             )