Fix invalid DataFrame column name validation before lowercasing.

python/tests/test_dataframe.py

@@ -26,6 +26,7 @@
 from tsfile import TsFileTableWriter, ColumnCategory
 from tsfile import to_dataframe
 from tsfile.exceptions import ColumnNotExistError, TypeMismatchError
+from tsfile.tsfile_table_writer import validate_dataframe_for_tsfile
 
 
 def convert_to_nullable_types(df):
@@ -318,3 +319,9 @@ def test_write_dataframe_empty():
     finally:
         if os.path.exists(tsfile_path):
             os.remove(tsfile_path)
+
+
+def test_validate_dataframe_none_column_name():
+    df = pd.DataFrame([[1, 2]], columns=[None, "value"])
+    with pytest.raises(ValueError, match="Column name cannot be None or empty"):
+        validate_dataframe_for_tsfile(df)

python/tsfile/tsfile_table_writer.py

@@ -34,6 +34,8 @@ def validate_dataframe_for_tsfile(df: pd.DataFrame) -> None:
     seen = set()
     duplicates = []
     for c in columns:
+        if c is None or (isinstance(c, str) and len(c) == 0):
+            raise ValueError("Column name cannot be None or empty")
         lower = c.lower()
         if lower in seen:
             duplicates.append(c)