Return all non-None ``hyperparameter`` values on ``obj`` as a ``dict[str,str].``

def serialize_all(obj):
        """Return all non-None ``hyperparameter`` values on ``obj`` as a ``dict[str,str].``"""
        if '_hyperparameters' not in dir(obj):
            return {}
        return {k: str(v) for k, v in obj._hyperparameters.items() if v is not None}