Don't crash on a blank PO-Revision-Date/POT-Creation-Date header

babel/messages/catalog.py

@@ -103,7 +103,12 @@ def _has_python_brace_format(string: str) -> bool:
     return field_name_seen
 
 
-def _parse_datetime_header(value: str) -> datetime.datetime:
+def _parse_datetime_header(value: str) -> datetime.datetime | None:
+    # Some tools (e.g. Poedit) leave the header's value blank instead of
+    # eliding the header, or leaving the "YEAR-MO-DA HO:MI+ZONE" placeholder.
+    if not value.strip():
+        return None
+
     match = re.match(r'^(?P<datetime>.*?)(?P<tzoffset>[+-]\d{4})?$', value)
 
     dt = datetime.datetime.strptime(match.group('datetime'), '%Y-%m-%d %H:%M')

tests/messages/test_catalog.py

@@ -15,6 +15,8 @@
 import pickle
 from io import StringIO
 
+import pytest
+
 from babel.dates import UTC, format_datetime
 from babel.messages import catalog, pofile
 from babel.util import FixedOffsetTimezone
@@ -556,6 +558,14 @@ def test_datetime_parsing():
     assert val2.tzinfo is None
 
 
+@pytest.mark.parametrize('value', ['', '   '])
+def test_datetime_parsing_blank_value_returns_none(value):
+    # Some tools (e.g. Poedit) leave the header blank instead of eliding
+    # it or using the "YEAR-MO-DA HO:MI+ZONE" placeholder; this used to
+    # raise ValueError from strptime instead of being treated as unset.
+    assert catalog._parse_datetime_header(value) is None
+
+
 def test_update_catalog_comments():
     # Based on https://web.archive.org/web/20100710131029/http://babel.edgewall.org/attachment/ticket/163/cat-update-comments.py