Apply pre-defined model masks.

def _model_mask(self, wavelengths=None):
        """
        Apply pre-defined model masks.
        """

        if wavelengths is None:
            wavelengths = self.wavelengths
        wavelengths = np.array(wavelengths)

        mask = np.ones_like(wavelengths, dtype=bool)
        model_mask = self._configuration.get("masks", {}).get("model", [])
        logger.debug("Applying model mask: {0}".format(model_mask))
        for start, end in model_mask:
            idx = np.clip(wavelengths.searchsorted([start, end]) + [0, 1], 0,
                wavelengths.size)
            mask[idx[0]:idx[1]] = False
        return mask