Properly handle user selection of `None` as vars_files (#31313)

* Properly handle user selection of `None` as vars_files

In a playbook, if a user has a playbook like:

```
- hosts: localhost
  connection: local
  vars_files:
  tasks:
  - ....
```

Then `vars_files` will be none, and cause a `TypeError` in vars-manager when it
tries to iterate over them. To avoid this, I changed the getter to either send
back the vars files from the user, or an empty list when the user passed
`None`.

* Only replace None with an empty list, not all falsey values

* Catch error when vars_files isn't iterable

* Move whole `for` loop into try/except and catch TypeError

* Line length

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/ansible/playbook/play.py b/lib/ansible/playbook/play.py
index 2fe4a9020d..ccd3b323a1 100644
--- a/lib/ansible/playbook/play.py
+++ b/lib/ansible/playbook/play.py
@@ -277,6 +277,8 @@ class Play(Base, Taggable, Become):
         return self.vars.copy()
 
     def get_vars_files(self):
+        if self.vars_files is None:
+            return []
         return self.vars_files
 
     def get_handlers(self):