code: def diff(self, first_row: List[Row], second_row: List[Row], column: NumberColumn) -> Number:
          
          if not first_row or not second_row:
              return 0.0  # type: ignore
          first_value = first_row[0].values[column.name]
          second_value = second_row[0].values[column.name]
          if isinstance(first_value, float) and isinstance(second_value, float):
              return first_value - second_value  # type: ignore
          else:
              raise ExecutionError(f"Invalid column for diff: {column.name}")
docs: Takes a two rows and a number column and returns the difference between the values under
          that column in those two rows.