handle groups correctly when they are 'null' (#41698)

* handle groups correctly when they are 'null'

 - even if defined as mapping but having no keys, objects shoudl still be processed correctly
 - also add ansilbe_verbosity to vars not to display in ansible-inventory

fixes #41692

lib/ansible/cli/inventory.py

@@ -42,6 +42,7 @@ INTERNAL_VARS = frozenset(['ansible_diff_mode',
                            'ansible_playbook_python',
                            'ansible_run_tags',
                            'ansible_skip_tags',
+                           'ansible_verbosity',
                            'ansible_version',
                            'inventory_dir',
                            'inventory_file',