code: public boolean voteDown(ParaObject obj, String voterid) {
  		if (obj == null || StringUtils.isBlank(voterid)) {
  			return false;
  		}
  		return getEntity(invokePatch(obj.getType().concat("/").concat(obj.getId()),
  				Entity.json(Collections.singletonMap("_votedown", voterid))), Boolean.class);
  	}
docs: Downvote an object and register the vote in DB.
  @param obj the object to receive -1 votes
  @param voterid the userid of the voter
  @return true if vote was successful