add replace_nan_value in NonValueTransformer reverse_convert

sdgx/data_processors/transformers/nan.py

@@ -137,9 +137,23 @@ def reverse_convert(self, processed_data: DataFrame) -> DataFrame:
 
         Does not require any action.
         """
-        logger.info("Data reverse-converted by NonValueTransformer (No Action).")
+        def replace_nan_value(df):
+            """
+            Scans all rows and columns in the DataFrame and replaces all cells with the value "NAN_VALUE", which is self.fill_na_value_default, with an empty string.
 
-        return processed_data
+            Parameters:
+            df (pd.DataFrame): The input DataFrame.
+
+            Returns:
+            pd.DataFrame: The DataFrame after replacement.
+            """
+            # Use the replace method of DataFrame to replace "NAN_VALUE" with an empty string
+            df_replaced = df.replace(self.fill_na_value_default, '')
+            return df_replaced
+
+        logger.info("Data reverse-converted by NonValueTransformer.")
+
+        return replace_nan_value(processed_data)
 
     pass