Validation failed on None, but the function accepts empty string and nothing

[JackLiang1272]

Is your feature request related to a problem? Please describe

prediction_path and event_path are consider required even when predictions_frame is populated. Because load_yml will populate the field with None in case like this , it will result in a validation error even if user is already providing the input when the predictions_frame.

Describe the solution you'd like

Make prediction_path and event_path optional. Or update load_yaml so it wouldn't populate the field with None.

Describe alternatives you've considered

Additional context