Do not error in case of empty list/dict constructed group

[AlanCoding]

SUMMARY

I had a case where a constructed (keyed_group) was templating from a certain hostvar, and it produced an empty list. It produced an error that didn't make any sense. This adds content to the error message and makes this use case work successfully.

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

constructed inventory plugin

ADDITIONAL INFORMATION

The error that my case produced, using devel, was:

 [WARNING]:  * Failed to parse /Users/alancoding/Documents/repos/ansible-inventory-file-examples/private/ec2/aws_ec2.yaml with auto plugin: No key or key resulted empty, invalid
entry

  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/inventory/manager.py", line 272, in parse_source
    plugin.parse(self._inventory, self._loader, source, cache=cache)
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/plugins/inventory/auto.py", line 58, in parse
    plugin.parse(inventory, loader, path, cache=cache)
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/plugins/inventory/aws_ec2.py", line 590, in parse
    self._populate(results, hostnames)
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/plugins/inventory/aws_ec2.py", line 490, in _populate
    self._add_hosts(hosts=groups[group], group=group, hostnames=hostnames)
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/plugins/inventory/aws_ec2.py", line 525, in _add_hosts
    self._add_host_to_keyed_groups(self.get_option('keyed_groups'), host, hostname, strict=strict)
  File "/Users/alancoding/Documents/repos/ansible/lib/ansible/plugins/inventory/__init__.py", line 432, in _add_host_to_keyed_groups
    raise AnsibleParserError("No key or key resulted empty, invalid entry")

In this case I was using tags.keys(), where the host variables had "tags": {}. It is going to be a problem if this case cannot be allowed to proceed.

Note: I only encountered this because I set strict: True, this allows users to be more vigilant, and I think it's a good idea to use this setting. However, it loses its utility if it fails the parsing process on cases it shouldn't.

Ping @bcoca @s-hertel

[AlanCoding]

For more background, I have isolated the host which returns "tags": {}

In the output from ec2.py, this host was a member of the tag_none group. That's a very non-standard syntax, so this will be produced via the compose groups, I'm still working on prototyping this. I'm 99% confident this will be created by another entry somewhere, and topic at issue here is to not error that host in the entry to create all the other tag group content.

[AlanCoding]

I'm not sure why the test says that it didn't pass. It doesn't show any failures.

[AlanCoding]

looks like it's good now