@Override
    public boolean equals(final Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        @SuppressWarnings("unchecked")
        final Pair<T1, T2> other = (Pair<T1, T2>) obj;
        if (first == null) {