Update get_login_url_and_token method in LoginUrlModel to handle …

…empty `ret_url` parameter

* Encode `ret_url` parameter as "%2F" if it is empty

d2x/models/sf/auth.py

@@ -180,7 +180,7 @@ class LoginUrlModel(CommonBaseModel):
 
     def get_login_url_and_token(self) -> tuple[str, str]:
         """Generate login URL and token"""
-        ret_url_encoded = urllib.parse.quote(self.ret_url)
+        ret_url_encoded = urllib.parse.quote(self.ret_url) if self.ret_url else "%2F"
         login_url_formatted = (
             f"{self.login_url}/secur/frontdoor.jsp?sid={self.access_token}&retURL={ret_url_encoded}"
         )