diff --git a/src/packaging/licenses/__init__.py b/src/packaging/licenses/__init__.py
index cebc6e6a..7f09dd96 100644
--- a/src/packaging/licenses/__init__.py
+++ b/src/packaging/licenses/__init__.py
@@ -49,8 +49,11 @@ class InvalidLicenseExpression(ValueError):
 
 
 def normalize_license_expression(raw_license_expression: str) -> str | None:
-    if not raw_license_expression:
-        return None
+    if raw_license_expression == "":
+        message = (
+            f"Invalid license expression: {raw_license_expression}"
+        )
+        raise InvalidLicenseExpression(message)
 
     license_refs = {
         ref.lower(): "LicenseRef-" + ref[11:]
diff --git a/tests/test_metadata.py b/tests/test_metadata.py
index e71e260e..5d8783e8 100644
--- a/tests/test_metadata.py
+++ b/tests/test_metadata.py
@@ -671,8 +671,6 @@ def test_optional_defaults_to_none(self, field_name):
             ("LicenseRef-Proprietary", "LicenseRef-Proprietary"),
             ("LicenseRef-Beerware-4.2", "LicenseRef-Beerware-4.2"),
             ("licenseref-beerware-4.2", "LicenseRef-beerware-4.2"),
-            ("", None),
-            (None, None),
         ],
     )
     def test_valid_license_expression(self, license_expression, expected):
@@ -684,6 +682,7 @@ def test_valid_license_expression(self, license_expression, expected):
     @pytest.mark.parametrize(
         "license_expression",
         [
+            "",
             "Use-it-after-midnight",
             "LicenseRef-License with spaces",
             "LicenseRef-License_with_underscores",