diff --git a/swh/lister/launchpad/lister.py b/swh/lister/launchpad/lister.py
index 4c66471..381106d 100644
--- a/swh/lister/launchpad/lister.py
+++ b/swh/lister/launchpad/lister.py
@@ -1,132 +1,132 @@
 # Copyright (C) 2020-2021  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
-from dataclasses import asdict, dataclass
+from dataclasses import dataclass
 from datetime import datetime
 import logging
 from typing import Any, Dict, Iterator, Optional
 
 import iso8601
 from launchpadlib.launchpad import Launchpad
 from lazr.restfulclient.resource import Collection
 
 from swh.scheduler.interface import SchedulerInterface
 from swh.scheduler.model import ListedOrigin
 
 from ..pattern import CredentialsType, Lister
 
 logger = logging.getLogger(__name__)
 
 LaunchpadPageType = Iterator[Collection]
 
 
 @dataclass
 class LaunchpadListerState:
     """State of Launchpad lister"""
 
     date_last_modified: Optional[datetime] = None
     """modification date of last updated repository since last listing"""
 
 
 class LaunchpadLister(Lister[LaunchpadListerState, LaunchpadPageType]):
     """
     List git repositories from Launchpad.
 
     Args:
         scheduler: instance of SchedulerInterface
         incremental: defines if incremental listing should be used, in that case
             only modified or new repositories since last incremental listing operation
             will be returned
     """
 
     LISTER_NAME = "launchpad"
 
     def __init__(
         self,
         scheduler: SchedulerInterface,
         incremental: bool = False,
         credentials: CredentialsType = None,
     ):
         super().__init__(
             scheduler=scheduler,
             url="https://launchpad.net/",
             instance="launchpad",
             credentials=credentials,
         )
         self.incremental = incremental
         self.date_last_modified = None
 
     def state_from_dict(self, d: Dict[str, Any]) -> LaunchpadListerState:
         date_last_modified = d.get("date_last_modified")
         if date_last_modified is not None:
             d["date_last_modified"] = iso8601.parse_date(date_last_modified)
         return LaunchpadListerState(**d)
 
     def state_to_dict(self, state: LaunchpadListerState) -> Dict[str, Any]:
-        d = asdict(state)
-        date_last_modified = d.get("date_last_modified")
+        d: Dict[str, Optional[str]] = {"date_last_modified": None}
+        date_last_modified = state.date_last_modified
         if date_last_modified is not None:
             d["date_last_modified"] = date_last_modified.isoformat()
         return d
 
     def get_pages(self) -> Iterator[LaunchpadPageType]:
         """
         Yields an iterator on all git repositories hosted on Launchpad sorted
         by last modification date in ascending order.
         """
         launchpad = Launchpad.login_anonymously(
             "softwareheritage", "production", version="devel"
         )
         date_last_modified = None
         if self.incremental:
             date_last_modified = self.state.date_last_modified
         get_repos = launchpad.git_repositories.getRepositories
         yield get_repos(
             order_by="most neglected first", modified_since_date=date_last_modified
         )
 
     def get_origins_from_page(self, page: LaunchpadPageType) -> Iterator[ListedOrigin]:
         """
         Iterate on all git repositories and yield ListedOrigin instances.
         """
         assert self.lister_obj.id is not None
 
         prev_origin_url = None
 
         for repo in page:
 
             origin_url = repo.git_https_url
 
             # filter out origins with invalid URL or origin previously listed
             # (last modified repository will be listed twice by launchpadlib)
             if not origin_url.startswith("https://") or origin_url == prev_origin_url:
                 continue
 
             last_update = repo.date_last_modified
 
             self.date_last_modified = last_update
 
             logger.debug("Found origin %s last updated on %s", origin_url, last_update)
 
             prev_origin_url = origin_url
 
             yield ListedOrigin(
                 lister_id=self.lister_obj.id,
                 visit_type="git",
                 url=origin_url,
                 last_update=last_update,
             )
 
     def finalize(self) -> None:
         if self.date_last_modified is None:
             return
 
         if self.incremental and (
             self.state.date_last_modified is None
             or self.date_last_modified > self.state.date_last_modified
         ):
             self.state.date_last_modified = self.date_last_modified
 
         self.updated = True