client: support optional date in Revision and Release

From the model specification, the date attribute in Revision and Release objects is optional. This commit handles the date attribute set to the None value.

It also tests the "typification" of a minimal Revision object to avoid regressions on this usecase.

---

Migrated from D2958 (view on Phabricator)

swh/web/client/tests/test_web_api_client.py

@@ -7,7 +7,8 @@ import json
 
 from dateutil.parser import parse as parse_date
 
-from swh.model.identifiers import parse_swhid
+from swh.model.identifiers import REVISION, parse_swhid
+from swh.web.client.client import typify_json
 
 from .api_data import API_DATA
 
@@ -172,3 +173,17 @@ def test_get_json(web_api_client, web_api_mock):
                 break
 
         assert actual == expected
+
+
+def test_typify_json_minimal_revision():
+    revision_data = {
+        "id": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+        "directory": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+        "date": None,
+        "committer_date": None,
+        "parents": [],
+    }
+    revision_typed = typify_json(revision_data, REVISION)
+    pid = "swh:1:rev:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+    assert revision_typed["id"] == parse_swhid(pid)
+    assert revision_typed["date"] is None