diff --git a/preprocessing/nextclade/src/loculus_preprocessing/processing_functions.py b/preprocessing/nextclade/src/loculus_preprocessing/processing_functions.py
index c04c63793..cc63d6229 100644
--- a/preprocessing/nextclade/src/loculus_preprocessing/processing_functions.py
+++ b/preprocessing/nextclade/src/loculus_preprocessing/processing_functions.py
@@ -232,8 +232,6 @@ def parse_date_into_range(
                 errors=[],
             )
 
-        logger.debug(f"release_date: {release_date}")
-
         formats_to_messages = {
             "%Y-%m-%d": None,
             "%Y-%m": "Day is missing. Assuming date is some time in the month.",
@@ -277,12 +275,6 @@ class DateRange:
                         date_range_lower=parsed_date.replace(month=1, day=1),
                         date_range_upper=parsed_date.replace(month=12, day=31),
                     )
-                case "_":
-                    datum = DateRange(
-                        date_range_string=None,
-                        date_range_lower=None,
-                        date_range_upper=max_upper_limit,
-                    )
 
             logger.debug(f"parsed_date: {datum}")
 
diff --git a/preprocessing/nextclade/tests/test_processing_functions.py b/preprocessing/nextclade/tests/test_processing_functions.py
index 6305baaef..3763a5585 100644
--- a/preprocessing/nextclade/tests/test_processing_functions.py
+++ b/preprocessing/nextclade/tests/test_processing_functions.py
@@ -483,27 +483,73 @@ def test_format_authors() -> None:
             raise AssertionError(msg)
 
 
-def test_parse_date_into_range():
-    assert ProcessingFunctions.parse_date_into_range(
-        {"date": "2021-12"}, "field_name", {"fieldType": "dateRangeString"}
-    ), "2021-12"
-    assert ProcessingFunctions.parse_date_into_range(
-        {"date": "2021-12"}, "field_name", {"fieldType": "dateRangeLower"}
-    ), "2021-12-01"
-    assert ProcessingFunctions.parse_date_into_range(
-        {"date": "2021-12"}, "field_name", {"fieldType": "dateRangeUpper"}
-    ), "2021-12-31"
-    assert ProcessingFunctions.parse_date_into_range(
-        {"date": "2021-02"}, "field_name", {"fieldType": "dateRangeUpper"}
-    ), "2021-02-28"
-    assert ProcessingFunctions.parse_date_into_range(
-        {"date": "2021"}, "field_name", {"fieldType": "dateRangeUpper"}
-    ), "2021-12-31"
-    assert ProcessingFunctions.parse_date_into_range(
-        {"date": "2021-12", "releaseDate": "2021-12-15"},
-        "field_name",
-        {"fieldType": "dateRangeUpper"},
-    ), "2021-12-15"
+def test_parse_date_into_range() -> None:
+    assert (
+        ProcessingFunctions.parse_date_into_range(
+            {"date": "2021-12"}, "field_name", {"fieldType": "dateRangeString"}
+        ).datum
+        == "2021-12"
+    ), "dateRangeString: 2021-12 should be returned as is."
+    assert (
+        ProcessingFunctions.parse_date_into_range(
+            {"date": "2021-12"}, "field_name", {"fieldType": "dateRangeLower"}
+        ).datum
+        == "2021-12-01"
+    ), "dateRangeLower: 2021-12 should be returned as 2021-12-01."
+    assert (
+        ProcessingFunctions.parse_date_into_range(
+            {"date": "2021-12"}, "field_name", {"fieldType": "dateRangeUpper"}
+        ).datum
+        == "2021-12-31"
+    ), "dateRangeUpper: 2021-12 should be returned as 2021-12-31."
+    assert (
+        ProcessingFunctions.parse_date_into_range(
+            {"date": "2021-02"}, "field_name", {"fieldType": "dateRangeUpper"}
+        ).datum
+        == "2021-02-28"
+    ), "dateRangeUpper: 2021-02 should be returned as 2021-02-28."
+    assert (
+        ProcessingFunctions.parse_date_into_range(
+            {"date": "2021"}, "field_name", {"fieldType": "dateRangeUpper"}
+        ).datum
+        == "2021-12-31"
+    ), "dateRangeUpper: 2021 should be returned as 2021-12-31."
+    assert (
+        ProcessingFunctions.parse_date_into_range(
+            {"date": "2021-12", "releaseDate": "2021-12-15"},
+            "field_name",
+            {"fieldType": "dateRangeUpper"},
+        ).datum
+        == "2021-12-15"
+    ), "dateRangeUpper: 2021-12 with releaseDate 2021-12-15 should be returned as 2021-12-15."
+    assert (
+        ProcessingFunctions.parse_date_into_range(
+            {"date": "", "releaseDate": "2021-12-15"},
+            "field_name",
+            {"fieldType": "dateRangeUpper"},
+        ).datum
+        == "2021-12-15"
+    ), "dateRangeUpper: empty date with releaseDate 2021-12-15 should be returned as 2021-12-15."
+    assert (
+        ProcessingFunctions.parse_date_into_range(
+            {"date": ""}, "field_name", {"fieldType": "dateRangeString"}
+        ).datum
+        is None
+    ), "dateRangeString: empty date should be returned as None."
+    assert (
+        ProcessingFunctions.parse_date_into_range(
+            {"date": "not.date"}, "field_name", {"fieldType": "dateRangeString"}
+        ).datum
+        is None
+    ), "dateRangeString: invalid date should be returned as None."
+    assert (
+        ProcessingFunctions.parse_date_into_range(
+            {"date": "", "releaseDate": "2021-12-15"},
+            "field_name",
+            {"fieldType": "dateRangeLower"},
+        ).datum
+        is None
+    ), "dateRangeLower: empty date should be returned as None."
 
 
 if __name__ == "__main__":