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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_rna(self) -> Rna: """Get the corresponding RNA or raise an exception if it's not the reference node. :raises: InferCentralDogmaException """

        if self.variants:
            raise InferCentralDogmaException('can not get rna for variant')

        return Rna(
            namespace=self.namespace,
            name=self.name,
            identifier=self.identifier
        )