code: def get_rna(self) -> Rna:
          
          if self.variants:
              raise InferCentralDogmaException('can not get rna for variant')
  
          return Rna(
              namespace=self.namespace,
              name=self.name,
              identifier=self.identifier
          )
docs: Get the corresponding RNA or raise an exception if it's not the reference node.
  
          :raises: InferCentralDogmaException