### Question:
ToLowerCaseFunction implements Function<String, String> { @Override public String apply(String input) { return input == null ? null : input.toLowerCase(); }  @Override String apply(String input);  }### Answer:
@Test public void test() { Assert.assertEquals("one", new ToLowerCaseFunction().apply("one")); Assert.assertEquals("one", new ToLowerCaseFunction().apply("One")); Assert.assertEquals("one", new ToLowerCaseFunction().apply("ONE")); Assert.assertEquals("", new ToLowerCaseFunction().apply("")); Assert.assertNull(new ToLowerCaseFunction().apply(null)); }