@Override
    public String toString() {
        long bit = nextSetBit(0);
        if (bit < 0) {
            return "{}";
        }

        final StringBuilder builder = new StringBuilder();
        builder.append("{");

        builder.append(Long.toString(bit));
        while ((bit = nextSetBit(bit + 1)) >= 0) {
            builder.append(", ");
            builder.append(Long.toString(bit));
        }
        builder.append("}");

        return builder.toString();
    }
Lowers {@link #wlen}, the number of words in use, by checking for trailing zero
words.
indexr-common/src/main/java/io/indexr/util/DirectBitMap.java