Add example

core-java-9/src/test/java/com/baeldung/java9/Java9OptionalsStreamTest.java

@@ -42,6 +42,19 @@ public class Java9OptionalsStreamTest {
         assertEquals("bar", filteredList.get(1));
     }
 
+    @Test
+    public void filterOutPresentOptionalsWithFlatMap2() {
+        assertEquals(4, listOfOptionals.size());
+
+        List<String> filteredList = listOfOptionals.stream()
+          .flatMap(o -> o.map(Stream::of).orElseGet(Stream::empty))
+          .collect(Collectors.toList());
+        assertEquals(2, filteredList.size());
+
+        assertEquals("foo", filteredList.get(0));
+        assertEquals("bar", filteredList.get(1));
+    }
+
     @Test
     public void filterOutPresentOptionalsWithJava9() {
         assertEquals(4, listOfOptionals.size());