code: def save(self, checkpoint):
      if self.model is None:
          raise Exception(
              "Needs to call fit_eval or restore first before calling save"
          )
      with open(checkpoint, "w") as fout:
          json.dump(model_to_json(self.model), fout)
  
imports: import json
  import numpy
  from prophet import Prophet
  from prophet.serialize import model_to_json, model_from_json
  from prophet.diagnostics import performance_metrics
  from prophet.diagnostics import cross_validation
  from zoo.orca.automl.metrics import Evaluator
  from zoo.orca.automl.model.abstract import BaseModel, ModelBuilder
label_desc: Use image node_id 7 for calling the ProphetModel obj's underlying member method code with example usage: obj.save(checkpoint) without return types