default logger does not write to file

csst_common/logger.py

@@ -10,9 +10,10 @@ Modified-History:
     2022-10-07, Bo Zhang, added Numpydoc docstring
 """
 import logging
+from typing import Optional
 
 
-def get_logger(name: str = "CSST pipeline", filename: str = "test.log"):
+def get_logger(name: str = "CSST pipeline", filename: Optional[str] = None):
     """
     Get a logger for CSST pipelines.
 
@@ -59,7 +60,7 @@ def get_logger(name: str = "CSST pipeline", filename: str = "test.log"):
     logger.addHandler(stream_handler)
 
     # file handler
-    if filename != "":
+    if filename is not None:
         file_handler = logging.FileHandler(filename=filename, encoding="utf-8")
         file_handler.setFormatter(formatter)
         file_handler.setLevel(logging.INFO)