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##### SUMMARY

The gcp dynamic inventory fails.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
- `gcp_compute`

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.8.3
  config file = /home/user/repos/project/ansible.cfg
  configured module search path = ['/home/user/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /home/user/.local/share/virtualenvs/project-ymgbqjq6/lib/python3.7/site-packages/ansible
  executable location = /home/user/.local/share/virtualenvs/project-ymgbqjq6/bin/ansible
  python version = 3.7.4 (default, Jul  9 2019, 03:52:42) [GCC 5.4.0 20160609]
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below
ANSIBLE_NOCOWS(/home/user/repos/project/ansible.cfg) = True
DEFAULT_ROLES_PATH(/home/user/repos/project/ansible.cfg) = ['/home/user/repos/project/roles']
DEFAULT_VAULT_PASSWORD_FILE(/home/user/repos/project/ansible.cfg) = /home/user/.secret/secret.txt
INVENTORY_ENABLED(/home/user/repos/project/ansible.cfg) = ['gcp_compute']
```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. target OS versions, network device firmware, etc. -->
- Ubuntu 16.04

##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->

Enable `gcp_compute` plugin in the inventory section of `ansible.cfg`:

```ini
[inventory]
enable_plugins = gcp_compute
```

Make `inventory.gcp.yml` file:

```yaml
plugin: gcp_compute
projects:
  - gcp-test-project-1245
auth_kind: serviceaccount
service_account_file: "~/.secret/gcp-test-project-1245.json"
```
Try to list inventories:

```sh
ansible-inventory --list -i inventory.gcp.yml
```

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->
JSON list of inventories.

##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->

<!--- Paste verbatim command output between quotes -->
```paste below
ansible-inventory 2.8.3
  config file = /home/user/repos/project/ansible.cfg
  configured module search path = ['/home/user/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /home/user/.local/share/virtualenvs/project-ymgbqjq6/lib/python3.7/site-packages/ansible
  executable location = /home/user/.local/share/virtualenvs/project-ymgbqjq6/bin/ansible-inventory
  python version = 3.7.4 (default, Jul  9 2019, 03:52:42) [GCC 5.4.0 20160609]
Using /home/user/repos/project/ansible.cfg as config file
setting up inventory plugins
 [WARNING]:  * Failed to parse /home/user/repos/project/inventory.gcp.yml with gcp_compute plugin: 'NoneType' object has no attribute 'get'

  File "/home/user/.local/share/virtualenvs/project-ymgbqjq6/lib/python3.7/site-packages/ansible/inventory/manager.py", line 268, in parse_source
    plugin.parse(self._inventory, self._loader, source, cache=cache)
  File "/home/user/.local/share/virtualenvs/project-ymgbqjq6/lib/python3.7/site-packages/ansible/plugins/inventory/gcp_compute.py", line 485, in parse
    for key, value in resp.get('items').items():

 [WARNING]: Unable to parse /home/user/repos/project/inventory.gcp.yml as an inventory source

 [WARNING]: No inventory was parsed, only implicit localhost is available

{
    "_meta": {
        "hostvars": {}
    },
    "all": {
        "children": [
            "ungrouped"
        ]
    }
}
```

use_contrib_script_compatible_sanitization:
          description:
            - By default this plugin is using a general group name sanitization to create safe and usable group names for use in Ansible.
              This option allows you to override that, in efforts to allow migration from the old inventory script.
            - For this to work you should also turn off the TRANSFORM_INVALID_GROUP_CHARS setting,
              otherwise the core engine will just use the standard sanitization on top.
            - This is not the default as such names break certain functionality as not all characters are valid Python identifiers
              which group names end up being used as.
          type: bool
          default: False
          version_added: '2.8'
        retrieve_image_info:
          description:
            - Populate the C(image) host fact for the instances returned with the GCP image name
            - By default this plugin does not attempt to resolve the boot image of an instance to the image name cataloged in GCP
              because of the performance overhead of the task.
            - Unless this option is enabled, the C(image) host variable will be C(null)
          type: bool
          default: False
          version_added: '2.8'
'''
EXAMPLES = '''
plugin: gcp_compute
zones: # populate inventory with instances in these regions
  - us-east1-a
projects:
  - gcp-prod-gke-100
  - gcp-cicd-101
filters:
  - machineType = n1-standard-1