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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_mutect_version(self):
 """Retrieve the Mutect version. """

        if self._mutect_version is None:
            mutect_jar = self._get_jar("muTect", ["mutect"])
            self._mutect_version = get_mutect_version(mutect_jar)
        return self._mutect_version