diff --git a/swh/clearlydefined/mapping_utils.py b/swh/clearlydefined/mapping_utils.py
--- a/swh/clearlydefined/mapping_utils.py
+++ b/swh/clearlydefined/mapping_utils.py
@@ -9,8 +9,6 @@
 import json
 from typing import Any, Dict, List, Optional, Tuple
 
-import attr
-
 from swh.clearlydefined.error import (
     InvalidComponents,
     NoJsonExtension,
@@ -45,14 +43,14 @@
 AUTHORITY = MetadataAuthority(
     type=MetadataAuthorityType.REGISTRY,
     url="https://clearlydefined.io/",
-    metadata={},
+    metadata=None,
 )
 
 
 FETCHER = MetadataFetcher(
     name="swh-clearlydefined",
     version="0.0.1",
-    metadata={},
+    metadata=None,
 )
 
 
@@ -73,8 +71,8 @@
         type=type,
         target=parse_swhid(swh_id),
         discovery_date=date,
-        authority=attr.evolve(AUTHORITY, metadata=None),
-        fetcher=attr.evolve(FETCHER, metadata=None),
+        authority=AUTHORITY,
+        fetcher=FETCHER,
         format=format,
         origin=origin.url if origin else None,
         metadata=json.dumps(metadata).encode("utf-8"),
diff --git a/swh/clearlydefined/tests/test_mapping_utils.py b/swh/clearlydefined/tests/test_mapping_utils.py
--- a/swh/clearlydefined/tests/test_mapping_utils.py
+++ b/swh/clearlydefined/tests/test_mapping_utils.py
@@ -8,7 +8,6 @@
 import json
 import os
 
-import attr
 import pytest
 
 from swh.clearlydefined.error import (
@@ -186,8 +185,8 @@
                     "swh:1:cnt:d81cc0710eb6cf9efd5b920a8453e1e07157b6cd"
                 ),
                 discovery_date=datetime(year=2021, month=2, day=6, tzinfo=timezone.utc),
-                authority=attr.evolve(AUTHORITY, metadata=None),
-                fetcher=attr.evolve(FETCHER, metadata=None),
+                authority=AUTHORITY,
+                fetcher=FETCHER,
                 format="clearlydefined-definition-json",
                 origin="http://central.maven.org/maven2/za/co/absa/cobrix/cobol-parser/"
                 "0.4.0/cobol-parser-0.4.0-sources.jar",
@@ -221,8 +220,8 @@
                     "swh:1:rev:4c66129b968ab8122964823d1d77677f50884cf6"
                 ),
                 discovery_date=datetime(year=2021, month=2, day=6, tzinfo=timezone.utc),
-                authority=attr.evolve(AUTHORITY, metadata=None),
-                fetcher=attr.evolve(FETCHER, metadata=None),
+                authority=AUTHORITY,
+                fetcher=FETCHER,
                 format="clearlydefined-definition-json",
                 origin="http://central.maven.org/maven2/za/co/absa/cobrix/cobol-parser/"
                 "0.4.0/cobol-parser-0.4.0-sources.jar",
@@ -258,8 +257,8 @@
                     "swh:1:cnt:d81cc0710eb6cf9efd5b920a8453e1e07157b6cd"
                 ),
                 discovery_date=datetime(year=2021, month=2, day=6, tzinfo=timezone.utc),
-                authority=attr.evolve(AUTHORITY, metadata=None),
-                fetcher=attr.evolve(FETCHER, metadata=None),
+                authority=AUTHORITY,
+                fetcher=FETCHER,
                 format="clearlydefined-harvest-scancode-json",
                 origin=None,
                 metadata=json.dumps(
@@ -294,8 +293,8 @@
                     "swh:1:cnt:d81cc0710eb6cf9efd5b920a8453e1e07157b6cd"
                 ),
                 discovery_date=datetime(year=2021, month=2, day=6, tzinfo=timezone.utc),
-                authority=attr.evolve(AUTHORITY, metadata=None),
-                fetcher=attr.evolve(FETCHER, metadata=None),
+                authority=AUTHORITY,
+                fetcher=FETCHER,
                 format="clearlydefined-harvest-scancode-json",
                 origin=None,
                 metadata=json.dumps(
@@ -330,8 +329,8 @@
                     "swh:1:cnt:36fade77193cb6d2bd826161a0979d64c28ab4fa"
                 ),
                 discovery_date=datetime(year=2021, month=2, day=6, tzinfo=timezone.utc),
-                authority=attr.evolve(AUTHORITY, metadata=None),
-                fetcher=attr.evolve(FETCHER, metadata=None),
+                authority=AUTHORITY,
+                fetcher=FETCHER,
                 format="clearlydefined-harvest-licensee-json",
                 origin=None,
                 metadata=json.dumps(
@@ -367,8 +366,8 @@
                     "swh:1:cnt:36fade77193cb6d2bd826161a0979d64c28ab4fa"
                 ),
                 discovery_date=datetime(year=2021, month=2, day=6, tzinfo=timezone.utc),
-                authority=attr.evolve(AUTHORITY, metadata=None),
-                fetcher=attr.evolve(FETCHER, metadata=None),
+                authority=AUTHORITY,
+                fetcher=FETCHER,
                 format="clearlydefined-harvest-licensee-json",
                 origin=None,
                 metadata=json.dumps(
@@ -404,8 +403,8 @@
                     "swh:1:cnt:36fade77193cb6d2bd826161a0979d64c28ab4fa"
                 ),
                 discovery_date=datetime(year=2021, month=2, day=6, tzinfo=timezone.utc),
-                authority=attr.evolve(AUTHORITY, metadata=None),
-                fetcher=attr.evolve(FETCHER, metadata=None),
+                authority=AUTHORITY,
+                fetcher=FETCHER,
                 format="clearlydefined-harvest-clearlydefined-json",
                 origin=None,
                 metadata=json.dumps(
@@ -420,8 +419,8 @@
                     "swh:1:cnt:d81cc0710eb6cf9efd5b920a8453e1e07157b6cd"
                 ),
                 discovery_date=datetime(year=2021, month=2, day=6, tzinfo=timezone.utc),
-                authority=attr.evolve(AUTHORITY, metadata=None),
-                fetcher=attr.evolve(FETCHER, metadata=None),
+                authority=AUTHORITY,
+                fetcher=FETCHER,
                 format="clearlydefined-harvest-clearlydefined-json",
                 origin=None,
                 metadata=json.dumps(
@@ -459,8 +458,8 @@
                     "swh:1:cnt:36fade77193cb6d2bd826161a0979d64c28ab4fa"
                 ),
                 discovery_date=datetime(year=2021, month=2, day=6, tzinfo=timezone.utc),
-                authority=attr.evolve(AUTHORITY, metadata=None),
-                fetcher=attr.evolve(FETCHER, metadata=None),
+                authority=AUTHORITY,
+                fetcher=FETCHER,
                 format="clearlydefined-harvest-clearlydefined-json",
                 origin=None,
                 metadata=json.dumps(
@@ -475,8 +474,8 @@
                     "swh:1:cnt:d81cc0710eb6cf9efd5b920a8453e1e07157b6cd"
                 ),
                 discovery_date=datetime(year=2021, month=2, day=6, tzinfo=timezone.utc),
-                authority=attr.evolve(AUTHORITY, metadata=None),
-                fetcher=attr.evolve(FETCHER, metadata=None),
+                authority=AUTHORITY,
+                fetcher=FETCHER,
                 format="clearlydefined-harvest-clearlydefined-json",
                 origin=None,
                 metadata=json.dumps(