code: def do_execute(self):
          
          inst = self.input.payload
          if not inst.has_class:
              return "No class set!"
  
          # load model?
          if self._model is None:
              model = None
              fname = str(self.resolve_option("model"))
              if os.path.isfile(fname):
                  model = serialization.read(fname)
              else:
                  name = self.resolve_option("storage_name")
                  if name in self.storagehandler.storage:
                      model = self.storagehandler.storage.get(name)
                      if isinstance(model, ModelContainer):
                          model = model.get("Model").jobject
              if model is None:
                  return "No model available from storage or serialized file!"
              self._is_classifier = is_instance_of(model, "weka.classifiers.Classifier")
              if self._is_classifier:
                  self._model = Classifier(jobject=model)
              else:
                  self._model = Clusterer(jobject=model)
  
          if self._is_classifier:
              cls = self._model.classify_instance(inst)
              dist = self._model.distribution_for_instance(inst)
              label = inst.class_attribute.value(int(cls))
              cont = ClassificationContainer(inst=inst, classification=cls, distribution=dist, label=label)
          else:
              cls = self._model.cluster_instance(inst)
              dist = self._model.distribution_for_instance(inst)
              cont = ClusteringContainer(inst=inst, cluster=int(cls), distribution=dist)
  
          self._output.append(Token(cont))
          return None
docs: The actual execution of the actor.
  
          :return: None if successful, otherwise error message
          :rtype: str