if (header == null)
throw new IllegalArgumentException("Entity tag is null");
try {
HttpHeaderReader reader = HttpHeaderReader.newInstance(header);
Event e = reader.next(false);
if (e == Event.QuotedString) {
return new EntityTag(reader.getEventValue());
} else if (e == Event.Token) {
if (reader.getEventValue().equals("W")) {
reader.nextSeparator('/');