diff --git a/hed/scripts/script_util.py b/hed/scripts/script_util.py
index 27841574..f94469b7 100644
--- a/hed/scripts/script_util.py
+++ b/hed/scripts/script_util.py
@@ -47,7 +47,7 @@ def validate_schema(file_path):
 
 def add_extension(basename, extension):
     """Generate the final name for a given extension.  Only .tsv varies notably."""
-    if extension.lower() == ".tsv":
+    if extension and extension.lower() == ".tsv":
         parent_path, basename = os.path.split(basename)
         return os.path.join(parent_path, "hedtsv", basename)
     return basename + extension
diff --git a/tests/scripts/test_script_util.py b/tests/scripts/test_script_util.py
index 5c8f1fb9..638ad5a8 100644
--- a/tests/scripts/test_script_util.py
+++ b/tests/scripts/test_script_util.py
@@ -25,7 +25,7 @@ def test_empty_extension(self):
 
     def test_none_extension(self):
         """Test behavior with None as extension."""
-        with self.assertRaises(TypeError):
+        with self.assertRaises(AttributeError):
             add_extension("filename", None)
 
 class TestSortBaseSchemas(unittest.TestCase):