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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def change_existence(self, is_hidden):
        # type: (bool) -> None
        '''
        Change the ISO9660 existence flag of this Directory Record.

        Parameters:
         is_hidden - True if this Directory Record should be hidden, False otherwise.
        Returns:
         Nothing.
        '''
        if not self._initialized:
            raise pycdlibexception.PyCdlibInternalError('Directory Record not yet initialized')

        if is_hidden:
            self.file_flags |= (1 << self.FILE_FLAG_EXISTENCE_BIT)
        else:
            self.file_flags &= ~(1 << self.FILE_FLAG_EXISTENCE_BIT)