Checks if an instance already exists in db with these kwargs else
        returns a new, saved instance of the service's model class.

        Args:
            **kwargs: instance parameters

def find_or_build(cls, **kwargs):
        """Checks if an instance already exists in db with these kwargs else
        returns a new, saved instance of the service's model class.

        Args:
            **kwargs: instance parameters
        """
        keys = kwargs.pop('keys') if 'keys' in kwargs else []
        return cls.first(**subdict(kwargs, keys)) or cls.build(**kwargs)