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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 get_ext(self, obj=None):
 """Return the file extension :param obj: the fileinfo with information. If None, this will use the stored object of JB_File :type obj: :class:`FileInfo` :returns: the file extension :rtype: str :raises: None """

        if obj is None:
            obj = self._obj
        return self._extel.get_ext(obj)