<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def initialise_modified_data(self):
 """ Initialise the modified_data if necessary """

        if self.__modified_data__ is None:
            if self.__original_data__:
                self.__modified_data__ = list(self.__original_data__)
            else:
                self.__modified_data__ = []