@Override
	public short getFirst() {
        // if the 0 key is in the set, then return it.
        if(containsKey((short)0)) {
            return (short)0;
        }
        // otherwise return the next key after 0.
        return getNext((short)0);
    }
Returns the first (lowest) key in the set.
Ghidra/Framework/Generic/src/main/java/ghidra/util/datastruct/BitTree.java