static ResourceData createNegativeRR(byte rrtype, long expiry) {
		switch (rrtype) {
		case Resolver.QTYPE_A:
			return new RR_A(null, 0, expiry);
		case Resolver.QTYPE_PTR:
			return new RR_PTR(null, 0, expiry);
		case Resolver.QTYPE_NS:
			return new RR_NS(null, null, expiry);
		case Resolver.QTYPE_MX:
			return new RR_MX(null, null, 0, expiry);
		case Resolver.QTYPE_SOA:
			return new RR_SOA(null, expiry, null, null, 0, 0, 0, 0, 0);
		case Resolver.QTYPE_SRV:
			return new RR_SRV(null, expiry, null, 0, 0, 0);
		case Resolver.QTYPE_TXT:
			return new RR_TXT(null, expiry, null);
		case Resolver.QTYPE_AAAA:
			return new RR_AAAA(null, null, expiry);
		case Resolver.QTYPE_CNAME:
			return new RR_CNAME(null, null, expiry);
		default:
			break;
		}
		throw new IllegalArgumentException("Unsupported RR type="+rrtype);
	}