diff --git a/swh/provenance/swhgraph/archive.py b/swh/provenance/swhgraph/archive.py
index 5424015..21d9fb9 100644
--- a/swh/provenance/swhgraph/archive.py
+++ b/swh/provenance/swhgraph/archive.py
@@ -1,41 +1,41 @@
 # Copyright (C) 2022  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 typing import Any, Dict, Iterable
 
 from swh.core.statsd import statsd
 from swh.model.model import Sha1Git
 from swh.model.swhids import CoreSWHID, ObjectType
 from swh.storage.interface import StorageInterface
 
 ARCHIVE_DURATION_METRIC = "swh_provenance_archive_graph_duration_seconds"
 
 
 class ArchiveGraph:
     def __init__(self, graph, storage: StorageInterface) -> None:
         self.graph = graph
         self.storage = storage  # required by ArchiveInterface
 
     @statsd.timed(metric=ARCHIVE_DURATION_METRIC, tags={"method": "directory_ls"})
     def directory_ls(self, id: Sha1Git, minsize: int = 0) -> Iterable[Dict[str, Any]]:
         raise NotImplementedError
 
     @statsd.timed(
         metric=ARCHIVE_DURATION_METRIC, tags={"method": "revision_get_parents"}
     )
     def revision_get_parents(self, id: Sha1Git) -> Iterable[Sha1Git]:
         src = CoreSWHID(object_type=ObjectType.REVISION, object_id=id)
         request = self.graph.neighbors(str(src), edges="rev:rev", return_types="rev")
 
-        yield from (CoreSWHID.from_string(swhid).object_id for swhid in request)
+        yield from (CoreSWHID.from_string(swhid).object_id for swhid in request if swhid)
 
     @statsd.timed(metric=ARCHIVE_DURATION_METRIC, tags={"method": "snapshot_get_heads"})
     def snapshot_get_heads(self, id: Sha1Git) -> Iterable[Sha1Git]:
         src = CoreSWHID(object_type=ObjectType.SNAPSHOT, object_id=id)
         request = self.graph.visit_nodes(
             str(src), edges="snp:rev,snp:rel,rel:rev", return_types="rev"
         )
 
-        yield from (CoreSWHID.from_string(swhid).object_id for swhid in request)
+        yield from (CoreSWHID.from_string(swhid).object_id for swhid in request if swhid)