diff --git a/base_external_system/README.rst b/base_external_system/README.rst
index c295a28a3..ea896c260 100644
--- a/base_external_system/README.rst
+++ b/base_external_system/README.rst
@@ -7,7 +7,7 @@ Base External System
    !! This file is generated by oca-gen-addon-readme !!
    !! changes will be overwritten.                   !!
    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-   !! source digest: sha256:95de33a7f2180cf65a752837bd7c9701f9bf08a5739cb302257b5ec8f2ed0181
+   !! source digest: sha256:199072a1b536548cfc88a3f85e558966096b960920cc11d93bdcbabcefc66bf3
    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
 .. |badge1| image:: https://img.shields.io/badge/maturity-Beta-yellow.png
diff --git a/base_external_system/models/external_system_adapter_os.py b/base_external_system/models/external_system_adapter_os.py
index e03634847..e1f31362b 100644
--- a/base_external_system/models/external_system_adapter_os.py
+++ b/base_external_system/models/external_system_adapter_os.py
@@ -13,11 +13,16 @@ class ExternalSystemAdapterOs(models.AbstractModel):
     system interface. This is still a fully usable implementation, however.
     """
 
+    __slots__ = ["previous_dir"]
+
     _name = "external.system.adapter.os"
     _inherit = "external.system.adapter"
     _description = "External System OS"
 
-    previous_dir = None
+    def __init__(self, name, bases, attrs):
+        """Declare previous_dir variable."""
+        super().__init__(name, bases, attrs)
+        self.previous_dir = None
 
     @api.model
     def external_get_client(self):
diff --git a/base_external_system/static/description/index.html b/base_external_system/static/description/index.html
index 3add662d8..f5e28bc5d 100644
--- a/base_external_system/static/description/index.html
+++ b/base_external_system/static/description/index.html
@@ -367,7 +367,7 @@ <h1 class="title">Base External System</h1>
 !! This file is generated by oca-gen-addon-readme !!
 !! changes will be overwritten.                   !!
 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-!! source digest: sha256:95de33a7f2180cf65a752837bd7c9701f9bf08a5739cb302257b5ec8f2ed0181
+!! source digest: sha256:199072a1b536548cfc88a3f85e558966096b960920cc11d93bdcbabcefc66bf3
 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! -->
 <p><a class="reference external image-reference" href="https://odoo-community.org/page/development-status"><img alt="Beta" src="https://img.shields.io/badge/maturity-Beta-yellow.png" /></a> <a class="reference external image-reference" href="http://www.gnu.org/licenses/lgpl-3.0-standalone.html"><img alt="License: LGPL-3" src="https://img.shields.io/badge/licence-LGPL--3-blue.png" /></a> <a class="reference external image-reference" href="https://github.com/OCA/server-backend/tree/16.0/base_external_system"><img alt="OCA/server-backend" src="https://img.shields.io/badge/github-OCA%2Fserver--backend-lightgray.png?logo=github" /></a> <a class="reference external image-reference" href="https://translation.odoo-community.org/projects/server-backend-16-0/server-backend-16-0-base_external_system"><img alt="Translate me on Weblate" src="https://img.shields.io/badge/weblate-Translate%20me-F47D42.png" /></a> <a class="reference external image-reference" href="https://runboat.odoo-community.org/builds?repo=OCA/server-backend&amp;target_branch=16.0"><img alt="Try me on Runboat" src="https://img.shields.io/badge/runboat-Try%20me-875A7B.png" /></a></p>
 <p>This module provides an interface/adapter mechanism for the definition