BUG: Request responses without the "Set-Cookie" header no longer overwrite the...

BUG: Request responses without the "Set-Cookie" header no longer overwrite the current auth_token with None

src/linkahead/connection/authentication/interface.py

@@ -125,8 +125,9 @@ class AbstractAuthenticator(ABC):
         Returns
         -------
         """
-        self.auth_token = parse_auth_token(
-            response.getheader("Set-Cookie"))
+        new_token = parse_auth_token(response.getheader("Set-Cookie"))
+        if new_token is not None:
+            self.auth_token = new_token
 
     def on_request(self, method: str, path: str, headers: QueryDict, **kwargs):
         # pylint: disable=unused-argument