diff --git a/pandasai/helpers/df_info.py b/pandasai/helpers/df_info.py
index ac3de91f3..a22dd5b90 100644
--- a/pandasai/helpers/df_info.py
+++ b/pandasai/helpers/df_info.py
@@ -11,7 +11,7 @@
     DataFrameType = Union[pd.DataFrame, str]
 
 
-def df_type(df: DataFrameType) -> str:
+def df_type(df: DataFrameType) -> Union[str, None]:
     """
     Returns the type of the dataframe.