diff --git a/swh/loader/package/archive/tests/test_archive.py b/swh/loader/package/archive/tests/test_archive.py
--- a/swh/loader/package/archive/tests/test_archive.py
+++ b/swh/loader/package/archive/tests/test_archive.py
@@ -73,10 +73,10 @@
 }
 
 _expected_branches_first_visit = {
-    "HEAD": {"target_type": "alias", "target": "releases/0.1.0",},
-    "releases/0.1.0": {
+    b"HEAD": {"target_type": "alias", "target": b"releases/0.1.0",},
+    b"releases/0.1.0": {
         "target_type": "revision",
-        "target": "44183488c0774ce3c957fa19ba695cf18a4a42b3",
+        "target": hash_to_bytes("44183488c0774ce3c957fa19ba695cf18a4a42b3"),
     },
 }
 
diff --git a/swh/loader/package/cran/tests/test_cran.py b/swh/loader/package/cran/tests/test_cran.py
--- a/swh/loader/package/cran/tests/test_cran.py
+++ b/swh/loader/package/cran/tests/test_cran.py
@@ -18,6 +18,7 @@
     parse_debian_control,
 )
 from swh.core.tarball import uncompress
+from swh.model.hashutil import hash_to_bytes
 from swh.model.model import TimestampWithTimezone
 
 from swh.loader.tests import (
@@ -177,9 +178,9 @@
     expected_snapshot = {
         "id": expected_snapshot_id,
         "branches": {
-            "HEAD": {"target": f"releases/{version}", "target_type": "alias"},
-            f"releases/{version}": {
-                "target": "42bdb16facd5140424359c8ce89a28ecfa1ce603",
+            b"HEAD": {"target": b"releases/2.22-6", "target_type": "alias"},
+            b"releases/2.22-6": {
+                "target": hash_to_bytes("42bdb16facd5140424359c8ce89a28ecfa1ce603"),
                 "target_type": "revision",
             },
         },
@@ -234,9 +235,9 @@
     expected_snapshot = {
         "id": expected_snapshot_id,
         "branches": {
-            "HEAD": {"target": f"releases/{version}", "target_type": "alias"},
-            f"releases/{version}": {
-                "target": "42bdb16facd5140424359c8ce89a28ecfa1ce603",
+            b"HEAD": {"target": b"releases/2.22-6", "target_type": "alias"},
+            b"releases/2.22-6": {
+                "target": hash_to_bytes("42bdb16facd5140424359c8ce89a28ecfa1ce603"),
                 "target_type": "revision",
             },
         },
diff --git a/swh/loader/package/debian/tests/test_debian.py b/swh/loader/package/debian/tests/test_debian.py
--- a/swh/loader/package/debian/tests/test_debian.py
+++ b/swh/loader/package/debian/tests/test_debian.py
@@ -27,6 +27,7 @@
 
 from swh.loader.package.debian.loader import resolve_revision_from
 
+from swh.model.hashutil import hash_to_bytes
 from swh.model.model import Person
 
 
@@ -135,9 +136,9 @@
     expected_snapshot = {
         "id": expected_snapshot_id,
         "branches": {
-            "releases/stretch/contrib/0.7.2-3": {
+            b"releases/stretch/contrib/0.7.2-3": {
                 "target_type": "revision",
-                "target": "2807f5b3f84368b4889a9ae827fe85854ffecf07",
+                "target": hash_to_bytes("2807f5b3f84368b4889a9ae827fe85854ffecf07"),
             }
         },
     }  # different than the previous loader as no release is done
@@ -180,9 +181,9 @@
     expected_snapshot = {
         "id": expected_snapshot_id,
         "branches": {
-            "releases/stretch/contrib/0.7.2-3": {
+            b"releases/stretch/contrib/0.7.2-3": {
                 "target_type": "revision",
-                "target": "2807f5b3f84368b4889a9ae827fe85854ffecf07",
+                "target": hash_to_bytes("2807f5b3f84368b4889a9ae827fe85854ffecf07"),
             }
         },
     }  # different than the previous loader as no release is done
@@ -382,13 +383,13 @@
     expected_snapshot = {
         "id": expected_snapshot_id,
         "branches": {
-            "releases/stretch/contrib/0.7.2-3": {
+            b"releases/stretch/contrib/0.7.2-3": {
                 "target_type": "revision",
-                "target": "2807f5b3f84368b4889a9ae827fe85854ffecf07",
+                "target": hash_to_bytes("2807f5b3f84368b4889a9ae827fe85854ffecf07"),
             },
-            "releases/buster/contrib/0.7.2-4": {
+            b"releases/buster/contrib/0.7.2-4": {
                 "target_type": "revision",
-                "target": "8224139c274c984147ef4b09aa0e462c55a10bd3",
+                "target": hash_to_bytes("8224139c274c984147ef4b09aa0e462c55a10bd3"),
             },
         },
     }
diff --git a/swh/loader/package/deposit/tests/test_deposit.py b/swh/loader/package/deposit/tests/test_deposit.py
--- a/swh/loader/package/deposit/tests/test_deposit.py
+++ b/swh/loader/package/deposit/tests/test_deposit.py
@@ -170,7 +170,7 @@
 
     revision_id = "637318680351f5d78856d13264faebbd91efe9bb"
     expected_branches = {
-        "HEAD": {"target": revision_id, "target_type": "revision",},
+        b"HEAD": {"target": hash_to_bytes(revision_id), "target_type": "revision",},
     }
 
     expected_snapshot = {
@@ -245,7 +245,9 @@
     assert_last_visit_matches(loader.storage, url, status="full", type="deposit")
 
     revision_id = "564d18943d71be80d0d73b43a77cfb205bcde96c"
-    expected_branches = {"HEAD": {"target": revision_id, "target_type": "revision"}}
+    expected_branches = {
+        b"HEAD": {"target": hash_to_bytes(revision_id), "target_type": "revision"}
+    }
     expected_snapshot = {
         "id": expected_snapshot_id,
         "branches": expected_branches,
diff --git a/swh/loader/package/loader.py b/swh/loader/package/loader.py
--- a/swh/loader/package/loader.py
+++ b/swh/loader/package/loader.py
@@ -144,13 +144,11 @@
         ]
         known_revisions = self.storage.revision_get(revs)
 
-        ret = {}
-        for revision in known_revisions:
-            if not revision:  # revision_get can return None
-                continue
-            ret[revision["id"]] = revision["metadata"]
-
-        return ret
+        return {
+            revision["id"]: revision["metadata"]
+            for revision in known_revisions
+            if revision
+        }
 
     def resolve_revision_from(
         self, known_artifacts: Dict, artifact_metadata: Dict
diff --git a/swh/loader/package/nixguix/tests/test_nixguix.py b/swh/loader/package/nixguix/tests/test_nixguix.py
--- a/swh/loader/package/nixguix/tests/test_nixguix.py
+++ b/swh/loader/package/nixguix/tests/test_nixguix.py
@@ -188,12 +188,12 @@
     )
 
     expected_branches = {
-        "evaluation": {
-            "target": "cc4e04c26672dd74e5fd0fecb78b435fb55368f7",
+        b"evaluation": {
+            "target": hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
             "target_type": "revision",
         },
-        "https://github.com/owner-1/repository-1/revision-1.tgz": {
-            "target": "488ad4e7b8e2511258725063cf43a2b897c503b4",
+        b"https://github.com/owner-1/repository-1/revision-1.tgz": {
+            "target": hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
             "target_type": "revision",
         },
     }
@@ -234,12 +234,12 @@
     )
 
     expected_branches = {
-        "evaluation": {
-            "target": "cc4e04c26672dd74e5fd0fecb78b435fb55368f7",
+        b"evaluation": {
+            "target": hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
             "target_type": "revision",
         },
-        "https://github.com/owner-1/repository-1/revision-1.tgz": {
-            "target": "488ad4e7b8e2511258725063cf43a2b897c503b4",
+        b"https://github.com/owner-1/repository-1/revision-1.tgz": {
+            "target": hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
             "target_type": "revision",
         },
     }
@@ -277,16 +277,16 @@
     # second time an url, because of the requests_mock_datadir_visits
     # fixture, the file has to end with `_visit1`.
     expected_branches = {
-        "evaluation": {
-            "target": "602140776b2ce6c9159bcf52ada73a297c063d5e",
+        b"evaluation": {
+            "target": hash_to_bytes("602140776b2ce6c9159bcf52ada73a297c063d5e"),
             "target_type": "revision",
         },
-        "https://github.com/owner-1/repository-1/revision-1.tgz": {
-            "target": "488ad4e7b8e2511258725063cf43a2b897c503b4",
+        b"https://github.com/owner-1/repository-1/revision-1.tgz": {
+            "target": hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
             "target_type": "revision",
         },
-        "https://github.com/owner-2/repository-1/revision-1.tgz": {
-            "target": "85e0bad74e33e390aaeb74f139853ae3863ee544",
+        b"https://github.com/owner-2/repository-1/revision-1.tgz": {
+            "target": hash_to_bytes("85e0bad74e33e390aaeb74f139853ae3863ee544"),
             "target_type": "revision",
         },
     }
@@ -336,12 +336,12 @@
     )
 
     expected_branches = {
-        "https://github.com/owner-1/repository-1/revision-1.tgz": {
-            "target": "488ad4e7b8e2511258725063cf43a2b897c503b4",
+        b"https://github.com/owner-1/repository-1/revision-1.tgz": {
+            "target": hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
             "target_type": "revision",
         },
-        "evaluation": {
-            "target": "cc4e04c26672dd74e5fd0fecb78b435fb55368f7",
+        b"evaluation": {
+            "target": hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
             "target_type": "revision",
         },
     }
@@ -368,8 +368,8 @@
     loader.load()
 
     expected_branches = {
-        "evaluation": {
-            "target": "cc4e04c26672dd74e5fd0fecb78b435fb55368f7",
+        b"evaluation": {
+            "target": hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
             "target_type": "revision",
         },
     }
@@ -416,12 +416,12 @@
     }
 
     expected_branches = {
-        "https://github.com/owner-1/repository-1/revision-1.tgz": {
-            "target": "488ad4e7b8e2511258725063cf43a2b897c503b4",
+        b"https://github.com/owner-1/repository-1/revision-1.tgz": {
+            "target": hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
             "target_type": "revision",
         },
-        "evaluation": {
-            "target": "cc4e04c26672dd74e5fd0fecb78b435fb55368f7",
+        b"evaluation": {
+            "target": hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
             "target_type": "revision",
         },
     }
@@ -522,7 +522,7 @@
         # mutate snapshot to create a clash
         snapshot["branches"][artifact_url.encode("utf-8")] = {
             "target_type": "revision",
-            "target": old_revision["id"],
+            "target": hash_to_bytes(old_revision["id"]),
         }
 
         # modify snapshot to actually change revision metadata structure so we simulate
diff --git a/swh/loader/package/npm/tests/test_npm.py b/swh/loader/package/npm/tests/test_npm.py
--- a/swh/loader/package/npm/tests/test_npm.py
+++ b/swh/loader/package/npm/tests/test_npm.py
@@ -325,17 +325,17 @@
     expected_snapshot = {
         "id": expected_snapshot_id,
         "branches": {
-            "HEAD": {"target": "releases/0.0.4", "target_type": "alias"},
-            "releases/0.0.2": {
-                "target": "d8a1c7474d2956ac598a19f0f27d52f7015f117e",
+            b"HEAD": {"target": b"releases/0.0.4", "target_type": "alias"},
+            b"releases/0.0.2": {
+                "target": hash_to_bytes("d8a1c7474d2956ac598a19f0f27d52f7015f117e"),
                 "target_type": "revision",
             },
-            "releases/0.0.3": {
-                "target": "5f9eb78af37ffd12949f235e86fac04898f9f72a",
+            b"releases/0.0.3": {
+                "target": hash_to_bytes("5f9eb78af37ffd12949f235e86fac04898f9f72a"),
                 "target_type": "revision",
             },
-            "releases/0.0.4": {
-                "target": "ba019b192bdb94bd0b5bd68b3a5f92b5acc2239a",
+            b"releases/0.0.4": {
+                "target": hash_to_bytes("ba019b192bdb94bd0b5bd68b3a5f92b5acc2239a"),
                 "target_type": "revision",
             },
         },
@@ -426,14 +426,14 @@
     expected_snapshot = {
         "id": "b11ebac8c9d0c9e5063a2df693a18e3aba4b2f92",
         "branches": {
-            "HEAD": {"target_type": "alias", "target": "releases/0.1.0"},
-            "releases/0.1.0": {
+            b"HEAD": {"target_type": "alias", "target": b"releases/0.1.0"},
+            b"releases/0.1.0": {
                 "target_type": "revision",
-                "target": "845673bfe8cbd31b1eaf757745a964137e6f9116",
+                "target": hash_to_bytes("845673bfe8cbd31b1eaf757745a964137e6f9116"),
             },
-            "releases/0.1.1-alpha.14": {
+            b"releases/0.1.1-alpha.14": {
                 "target_type": "revision",
-                "target": "05181c12cd8c22035dd31155656826b85745da37",
+                "target": hash_to_bytes("05181c12cd8c22035dd31155656826b85745da37"),
             },
         },
     }
@@ -558,10 +558,10 @@
     expected_snapshot = {
         "id": "d6e08e19159f77983242877c373c75222d5ae9dd",
         "branches": {
-            "HEAD": {"target_type": "alias", "target": "releases/0.0.1"},
-            "releases/0.0.1": {
+            b"HEAD": {"target_type": "alias", "target": b"releases/0.0.1"},
+            b"releases/0.0.1": {
                 "target_type": "revision",
-                "target": "9e4dd2b40d1b46b70917c0949aa2195c823a648e",
+                "target": hash_to_bytes("9e4dd2b40d1b46b70917c0949aa2195c823a648e"),
             },
         },
     }
diff --git a/swh/loader/package/pypi/tests/test_pypi.py b/swh/loader/package/pypi/tests/test_pypi.py
--- a/swh/loader/package/pypi/tests/test_pypi.py
+++ b/swh/loader/package/pypi/tests/test_pypi.py
@@ -373,11 +373,11 @@
     assert list(loader.storage.revision_missing(expected_revs)) == []
 
     expected_branches = {
-        "releases/1.2.0": {
-            "target": "e445da4da22b31bfebb6ffc4383dbf839a074d21",
+        b"releases/1.2.0": {
+            "target": hash_to_bytes("e445da4da22b31bfebb6ffc4383dbf839a074d21"),
             "target_type": "revision",
         },
-        "HEAD": {"target": "releases/1.2.0", "target_type": "alias",},
+        b"HEAD": {"target": b"releases/1.2.0", "target_type": "alias",},
     }
 
     expected_snapshot = {
@@ -454,15 +454,15 @@
     assert list(loader.storage.revision_missing(expected_revs)) == []
 
     expected_branches = {
-        "releases/1.1.0": {
-            "target": "4c99891f93b81450385777235a37b5e966dd1571",
+        b"releases/1.1.0": {
+            "target": hash_to_bytes("4c99891f93b81450385777235a37b5e966dd1571"),
             "target_type": "revision",
         },
-        "releases/1.2.0": {
-            "target": "e445da4da22b31bfebb6ffc4383dbf839a074d21",
+        b"releases/1.2.0": {
+            "target": hash_to_bytes("e445da4da22b31bfebb6ffc4383dbf839a074d21"),
             "target_type": "revision",
         },
-        "HEAD": {"target": "releases/1.2.0", "target_type": "alias",},
+        b"HEAD": {"target": b"releases/1.2.0", "target_type": "alias",},
     }
 
     expected_snapshot = {
@@ -504,15 +504,15 @@
     } == stats
 
     expected_branches = {
-        "releases/1.1.0": {
-            "target": "4c99891f93b81450385777235a37b5e966dd1571",
+        b"releases/1.1.0": {
+            "target": hash_to_bytes("4c99891f93b81450385777235a37b5e966dd1571"),
             "target_type": "revision",
         },
-        "releases/1.2.0": {
-            "target": "e445da4da22b31bfebb6ffc4383dbf839a074d21",
+        b"releases/1.2.0": {
+            "target": hash_to_bytes("e445da4da22b31bfebb6ffc4383dbf839a074d21"),
             "target_type": "revision",
         },
-        "HEAD": {"target": "releases/1.2.0", "target_type": "alias",},
+        b"HEAD": {"target": b"releases/1.2.0", "target_type": "alias",},
     }
 
     expected_snapshot = {
@@ -642,19 +642,19 @@
     assert list(loader.storage.revision_missing(expected_revs)) == []
 
     expected_branches = {
-        "releases/1.1.0": {
-            "target": "4c99891f93b81450385777235a37b5e966dd1571",
+        b"releases/1.1.0": {
+            "target": hash_to_bytes("4c99891f93b81450385777235a37b5e966dd1571"),
             "target_type": "revision",
         },
-        "releases/1.2.0": {
-            "target": "e445da4da22b31bfebb6ffc4383dbf839a074d21",
+        b"releases/1.2.0": {
+            "target": hash_to_bytes("e445da4da22b31bfebb6ffc4383dbf839a074d21"),
             "target_type": "revision",
         },
-        "releases/1.3.0": {
-            "target": "51247143b01445c9348afa9edfae31bf7c5d86b1",
+        b"releases/1.3.0": {
+            "target": hash_to_bytes("51247143b01445c9348afa9edfae31bf7c5d86b1"),
             "target_type": "revision",
         },
-        "HEAD": {"target": "releases/1.3.0", "target_type": "alias",},
+        b"HEAD": {"target": b"releases/1.3.0", "target_type": "alias",},
     }
     expected_snapshot = {
         "id": expected_snapshot_id2,
@@ -700,12 +700,12 @@
     }
 
     expected_branches = {
-        "releases/1.1.0/nexter-1.1.0.zip": {
-            "target": "4c99891f93b81450385777235a37b5e966dd1571",
+        b"releases/1.1.0/nexter-1.1.0.zip": {
+            "target": hash_to_bytes("4c99891f93b81450385777235a37b5e966dd1571"),
             "target_type": "revision",
         },
-        "releases/1.1.0/nexter-1.1.0.tar.gz": {
-            "target": "0bf88f5760cca7665d0af4d6575d9301134fe11a",
+        b"releases/1.1.0/nexter-1.1.0.tar.gz": {
+            "target": hash_to_bytes("0bf88f5760cca7665d0af4d6575d9301134fe11a"),
             "target_type": "revision",
         },
     }
diff --git a/swh/loader/tests/test_init.py b/swh/loader/tests/test_init.py
--- a/swh/loader/tests/test_init.py
+++ b/swh/loader/tests/test_init.py
@@ -386,7 +386,10 @@
     unexpected_snapshot = {
         "id": "2498dbf535f882bc7f9a18fb16c9ad27fda7bab7",  # id is correct
         "branches": {
-            "master": {"target": hash_hex, "target_type": "release",}  # wrong branch
+            b"master": {
+                "target": hash_to_bytes(hash_hex),  # wrong branch
+                "target_type": "release",
+            }
         },
     }