@Override
    public Integer convert(String source) {
        return isNotEmpty(source) ? valueOf(source) : null;
    }
@Test
    void testConvert() {
        assertEquals(Integer.valueOf("1"), converter.convert("1"));
        assertNull(converter.convert(null));
        assertThrows(NumberFormatException.class, () -> {
            converter.convert("ttt");
        });
    }