diff --git a/superset/connectors/sqla/models.py b/superset/connectors/sqla/models.py
index e236cffcee98c..4561cbf7ce298 100644
--- a/superset/connectors/sqla/models.py
+++ b/superset/connectors/sqla/models.py
@@ -833,7 +833,7 @@ def __repr__(self) -> str:
 
     @validates("python_date_format")
     def validate_pdf_is_iso8601(self, _: str, dt_format: str) -> str:
-        if dt_format in ("epoch_s", "epoch_ms"):
+        if dt_format in ("epoch_s", "epoch_ms", None):
             return dt_format
         try:
             dt_str = datetime.now().strftime(dt_format)