@Override
    public String toString() {
        //if (this == SOME) {
        //    return "SOME";
        //} else
        if (this == ALL) {
            return "ALL";
        } else if (this == NONE) {
            return "NONE";
        } else {
            String s = agent.toString();
            return s.substring(0, Math.min(s.length(), 8));
        }
    }
A wrapper of the underlying bitmap.

We guarantee that the content of {@link #ALL} or {@link #NONE} will never be changed.
As those static instances are shared around.
indexr-common/src/main/java/io/indexr/util/BitMap.java