public String encode(long... numbers) {
        if (numbers.length == 0) {
            return "";
        }

        for (final long number : numbers) {
            if (number < 0) {
                return "";
            }
            if (number > MAX_NUMBER) {
                throw new IllegalArgumentException("number can not be greater than " + MAX_NUMBER + "L");
            }
        }
        return this._encode(numbers);
    }
@Test
    public void test_randomness_for_incrementing() {
        Hashids a;
        a = new Hashids("this is my salt");
        Assert.assertEquals(a.encode(1L), "NV");
        Assert.assertEquals(a.encode(2L), "6m");
        Assert.assertEquals(a.encode(3L), "yD");
        Assert.assertEquals(a.encode(4L), "2l");
        Assert.assertEquals(a.encode(5L), "rD");
    }