Merged for javadoc

mug/src/main/java/com/google/mu/util/stream/MoreStreams.java

@@ -475,6 +475,28 @@ public static <T> Stream<T> whileNotNull(Supplier<? extends T> supplier) {
         false);
   }
 
+  /**
+   * Returns a Stream wrapping {@code element} if it's not null; otherwise empty.
+   *
+   * <p>Useful if you'll chain it with further {@code flatMap()}, {@code anyMatch()} etc. For
+   * example:
+   *
+   * <pre>{@code
+   * boolean hasKeyword =
+   *     MoreStreams.ifNotNull(type.getAnnotation(MyAnnotation.class))
+   *         .flatMap(annotation -> annotation.keywords().stream())
+   *         .anyMatch(currentKeyword::equals);
+   * }</pre>
+   *
+   * <p>It's the Stream counterpart of {@link java.util.Optional#ofNullable}, and is more concise
+   * and efficient than {@code Optional.ofNullable(element).stream()}.
+   *
+   * @since 8.1
+   */
+  public static <T> Stream<T> ifNotNull(T element) {
+    return element == null ? Stream.empty() : Stream.of(element);
+  }
+
   /**
    * Returns a sequential stream with {@code sideEfect} attached on every element.
    *

mug/src/test/java/com/google/mu/util/stream/MoreStreamsTest.java

@@ -346,7 +346,7 @@ public class MoreStreamsTest {
   @Test public void testNulls() throws Exception {
     NullPointerTester tester = new NullPointerTester();
     asList(MoreStreams.class.getDeclaredMethods()).stream()
-        .filter(m -> m.getName().equals("generate"))
+        .filter(m -> m.getName().equals("generate") || m.getName().equals("ifNotNull"))
         .forEach(tester::ignore);
     tester.testAllPublicStaticMethods(MoreStreams.class);
   }
@@ -387,4 +387,14 @@ public class MoreStreamsTest {
         .containsExactly(10, 2L, 9, 3L, 8, 1L)
         .inOrder();
   }
+
+  @Test public void testIfNotNull_fromNull() {
+    Object element = null;
+    assertThat(MoreStreams.ifNotNull(element)).isEmpty();
+  }
+
+  @Test public void testIfNotNull_fromNonNull() {
+    Object element = 1;
+    assertThat(MoreStreams.ifNotNull(element)).containsExactly(1);
+  }
 }