Validator to ensure proper usage.

def _check_min_density(self, min_density):
        """Validator to ensure proper usage."""

        if min_density is None:
            self._min_density = -np.Inf
        elif (isinstance(min_density, float) and (0.0 <= min_density < 1.0)):
            self._min_density = min_density
        else:
            raise ValueError('min_density must be float and be >=0.0 and < 1.0')