Fix IgnoreComparatorUnitTest.

Using smart nulls in the mock causes the String methods to return "" rather than null, which is more consistent with the use of default values in the annotation declaration.

java/client/test/org/openqa/selenium/testing/drivers/IgnoreComparatorUnitTest.java

@@ -31,6 +31,7 @@
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
+import org.mockito.Mockito;
 import org.openqa.selenium.Platform;
 import org.openqa.selenium.testing.Driver;
 import org.openqa.selenium.testing.Ignore;
@@ -127,9 +128,9 @@ public void shouldIgnoreDisabledNativeEventsIfIgnoringAll() {
 
   private IgnoreList ignoreForDriver(final Set<Driver> drivers,
                                     final Set<Platform> platforms) {
-    final IgnoreList ignore = mock(IgnoreList.class);
+    final IgnoreList ignore = mock(IgnoreList.class, Mockito.RETURNS_SMART_NULLS);
     final Ignore[] list = drivers.stream().map(driver -> {
-      Ignore ig = mock(Ignore.class);
+      Ignore ig = mock(Ignore.class, Mockito.RETURNS_SMART_NULLS);
       when(ig.value()).thenReturn(driver);
       return ig;
     }).collect(Collectors.toList()).toArray(new Ignore[drivers.size()]);