firstKey

Returns the smallest key in the map. Returns null if the map is empty.

Example:

    var map = new TreeMap<string,string> ((a, b) => {
        return strcmp (a, b);
    });
    map.put ("b", "2");
    map.put ("a", "1");
    assert (map.firstKey () == "a");

Returns:

the smallest key, or null if empty.