Can You Make A Ransom Note From A Magazine?

boolean ransom(String note, String magazine) {
    if (note == null || magazine == null) throw new NullPointerException();
    if (note.length() == 0) return true;
    if (magazine.length() == 0 || magazine.length() < note.length()) return false;
    char[] cs = note.toCharArray();
    Map<Char, Integer> m = new HashMap<Char, Integer>();
    for (char c: cs)
        if (m.containsKey(c)) m.put(c, m.get(c) + 1);
        else m.put(c, 1);
    cs = magazine.toCharArray();
    for (char c: cs)
        if (m.containsKey(c)) {
            int i = m.get(c);
            if (i == 1) {
                m.remove(c);
                if (m.isEmpty()) break;
            } else m.put(c, i - 1);
        }
    return m.isEmpty();
}