[Core] Missing prediction_intervals attribute when saving the NeuralForecast model

[JQGoh]

What happened + What you expected to happen

Error message reported

File "/opt/conda/lib/python3.10/runpy.py", line 196, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/opt/conda/lib/python3.10/runpy.py", line 86, in _run_code
exec(code, run_globals)
File "/opt/conda/lib/python3.10/site-packages/kfp/dsl/executor_main.py", line 109, in <module>
executor_main()
File "/opt/conda/lib/python3.10/site-packages/kfp/dsl/executor_main.py", line 101, in executor_main
output_file = executor.execute()
File "/opt/conda/lib/python3.10/site-packages/kfp/dsl/executor.py", line 361, in execute
result = self.func(**func_kwargs)
File "/tmp/tmp.mkcsWMcuA9/ephemeral_component.py", line 251, in train_neural_network
nf.save(path=model_artifact.path, model_index=None, overwrite=True, save_dataset=True)
File "/opt/conda/lib/python3.10/site-packages/neuralforecast/core.py", line 1537, in save
"prediction_intervals": self.prediction_intervals,
AttributeError: 'NeuralForecast' object has no attribute 'prediction_intervals'

Versions / Dependencies

NeuralForecast model 1.7.6

Reproduction script

To reproduce this: Use a saved model trained prior to the version of 1.7.6.
Load this old model and try to save it again.

Issue Severity

Low: It annoys or frustrates me.