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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 _append_unknown_char(self):
        '''
        Appends the unknown character, in case one was encountered.
        '''
        if self.unknown_strategy == UNKNOWN_INCLUDE and \
           self.unknown_char is not None:
            self._append_to_stack(self.unknown_char)

        self.unknown_char = None