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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 writejar(self, jar):
 """Schedules all entries from the given ``jar``'s to be added to this jar save for the manifest. :param string jar: the path to the pre-existing jar to graft into this jar """

    if not jar or not isinstance(jar, string_types):
      raise ValueError('The jar path must be a non-empty string')

    self._jars.append(jar)