if (a.kind > b.kind) {
if (a.kind < b.kind) {
	public static IsNullValue merge(IsNullValue a, IsNullValue b) {		// Left hand value should be smaller.		if (a.kind > b.kind) {			IsNullValue tmp = a;			a = b;			b = tmp;		}		int result = mergeMatrix[a.kind][b.kind];		assert result >= 0;		return instanceList[result];	}