Parse the JSON, return a slug in the form '{subtype}-{first ottid}-{last-ottid}'.

def _build_amendment_id(self, json_repr):
        """Parse the JSON, return a slug in the form '{subtype}-{first ottid}-{last-ottid}'."""
        amendment = self._coerce_json_to_amendment(json_repr)
        if amendment is None:
            return None
        amendment_subtype = 'additions'
        # TODO: Look more deeply once we have other subtypes!
        first_ottid = amendment['TODO']
        last_ottid = amendment['TODO']
        return slugify('{s}-{f}-{l}'.format(s=amendment_subtype, f=first_ottid, l=last_ottid))