### Question:
CbStrings { public static String emptyToNull(String s) { return isNullOrEmpty(s) ? null : s; } private  CbStrings(); static String nullToEmpty(String s); static String emptyToNull(String s); static boolean isNullOrEmpty(String s); static String removeStart(String s, String removeMe); static String removeEnd(String s, String removeMe);  }### Answer:
@Test void emptyToNull() { assertNull(CbStrings.emptyToNull(null)); assertNull(CbStrings.emptyToNull("")); assertEquals("xyzzy", CbStrings.emptyToNull("xyzzy")); }