When a Trainer instance calls the _save_model method and self.features_transform has transform keys with not-None values, it raises: AttributeError: 'NoneType' object has no attribute 'group'. We didn't notice because even if we are widely testing features_transform usage within the dataset.py quite broadly, we're not doing that with the trainer.py-related usage. We should:

• Fix the bug and add tests fix: features transform in Trainer._save_model internal method #573
• Make a new patch release release: patch 3.0.1 #574