### Question:
Strings { public static String nullToEmpty(String s) { return s == null ? "" : s; }  static String nullToEmpty(String s); static boolean isNullOrEmpty(String s);  }### Answer:
@Test public void testNullToEmpty() { Assert.assertEquals("", Strings.nullToEmpty(null)); Assert.assertEquals("", Strings.nullToEmpty("")); Assert.assertEquals("abc", Strings.nullToEmpty("abc")); }