public static String substringBetween(String s, String open, String close) {
        if (s.contains(open) && s.contains(close)) {
            return substringBefore(substringAfter(s, open), close);
        }
        return null;
    }
@Test
    void testSubstringBetween() {
        assertThat(substringBetween("${some.string}", "${", "}")).isEqualTo("some.string");
        assertThat(substringBetween("some.string", "${", "}")).isNull();
    }