No good way to transform an immutable map

Transform.java

    private static <K1, K2, V1, V2> Map<K2, V2> transform(Map<K1, V1> map, Function<K1, K2> keyTransform, Function<V1, V2> valueTransform) {
        Iterator<Map.Entry<K1, V1>> iterator = map.entrySet().iterator();
        if (! iterator.hasNext()) {
            return Map.of();
        }
        Map.Entry<K1, V1> entry = iterator.next();
        K2 k1 = keyTransform.apply(entry.getKey());
        V2 v1 = valueTransform.apply(entry.getValue());
        if (! iterator.hasNext()) {
            return Map.of(k1, v1);
        }
        entry = iterator.next();
        K2 k2 = keyTransform.apply(entry.getKey());
        V2 v2 = valueTransform.apply(entry.getValue());
        if (! iterator.hasNext()) {
            return Map.of(k1, v1, k2, v2);
        }
        // ...etc...
    }