public TSIGRecord
getTSIG() {
	int count = header.getCount(Section.ADDITIONAL);
	if (count == 0)
		return null;
	List l = sections[Section.ADDITIONAL];
	Record rec = (Record) l.get(count - 1);
	if (rec.type !=  Type.TSIG)
		return null;
	return (TSIGRecord) rec;
}
Returns the TSIG record from the ADDITIONAL section, if one is present.
@see TSIGRecord
@see TSIG
@see Section
src/main/java/core/org/xbill/DNS/Message.java