FIX

@@ -563,7 +563,9 @@ class BSWorkbook(Workbook):
                 outlay_cell = None if outlay_cell_idx is None or outlay_cell_idx >= length else rows[outlay_cell_idx]
                 borrow_cell = None if borrow_cell_idx is None or borrow_cell_idx >= length else rows[borrow_cell_idx]
 
-                summary_cell_value = None if summary_cell is None else summary_cell.value.strip()
+                summary_cell_value = None if summary_cell is None else summary_cell.value
+                if summary_cell.value is not None:
+                    summary_cell_value = summary_cell_value.strip()
                 date_cell_value = None if date_cell is None else date_cell.value
                 amount_cell_value = None if amount_cell is None else amount_cell.value
                 over_cell_value = None if over_cell is None else over_cell.value