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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 poster_frame(self):
 """Return |Image| object containing poster frame for this movie. Returns |None| if this movie has no poster frame (uncommon). """

        slide_part, rId = self.part, self._element.blip_rId
        if rId is None:
            return None
        return slide_part.get_image(rId)