Fix error using jsonfile with incomplete config (#17567)

If 'fact_caching=jsonfile' was configured, but
'fact_caching_connection' was not configured, jsonfile
would fail and ansible-playbook would exit with a traceback.

Fixes #17566

lib/ansible/plugins/cache/jsonfile.py

@@ -50,7 +50,11 @@ class CacheModule(BaseCacheModule):
 
         self._timeout = float(C.CACHE_PLUGIN_TIMEOUT)
         self._cache = {}
-        self._cache_dir = os.path.expanduser(os.path.expandvars(C.CACHE_PLUGIN_CONNECTION))
+        self._cache_dir = None
+
+        if C.CACHE_PLUGIN_CONNECTION:
+            # expects a dir path
+            self._cache_dir = os.path.expanduser(os.path.expandvars(C.CACHE_PLUGIN_CONNECTION))
 
         if not self._cache_dir:
             raise AnsibleError("error, 'jsonfile' cache plugin requires the 'fact_caching_connection' config option to be set (to a writeable directory path)")