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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 is_manifest_valid(self, manifest_id):
 """Check validation shortcut :param: manifest_id (string) id received in :method:`validate_manifest` :returns: * True if manifest was valid * None if manifest wasn't checked yet * validation dict if not valid """

        response = self.get_manifest_validation_result(manifest_id)
        if response.status_code != 200:
            raise Exception(response.status_code)
        content = json.loads(response.content)
        if not content['processed']:
            return None
        if content['valid']:
            return True
        return content['validation']