public static String substringAfter(String s, String splitter) {
        final int indexOf = s.indexOf(splitter);
        return indexOf >= 0 ? s.substring(indexOf + splitter.length()) : null;
    }
@Test
    void testSubstringAfterSplitterSingleChar() {
        assertThat(substringAfter("15", "-")).isNull();
        assertThat(substringAfter("15-ea", "-")).isEqualTo("ea");
    }