Remove unnecessary check for currentMediaItem in legacy session stub

This check was a leftover from when the metadata was generated from
the MediaItem only. Since we moved to the actual MediaMetadata fields,
the check is completely unnecessary and prevents accessing metadata
when the GET_CURRENT_MEDIA_ITEM command is not available.

PiperOrigin-RevId: 524837587
(cherry picked from commit e0bb23d4)

libraries/session/src/main/java/androidx/media3/session/MediaSessionLegacyStub.java

@@ -1321,11 +1321,6 @@ import org.checkerframework.checker.nullness.compatqual.NullableType;
       lastMediaMetadata = newMediaMetadata;
       lastDurationMs = newDurationMs;
 
-      if (currentMediaItem == null) {
-        setMetadata(sessionCompat, /* metadataCompat= */ null);
-        return;
-      }
-
       @Nullable Bitmap artworkBitmap = null;
       ListenableFuture<Bitmap> bitmapFuture =
           sessionImpl.getBitmapLoader().loadBitmapFromMetadata(newMediaMetadata);

libraries/test_session_current/src/androidTest/java/androidx/media3/session/MediaControllerCompatCallbackWithMediaSessionTest.java

@@ -1085,8 +1085,9 @@ public class MediaControllerCompatCallbackWithMediaSessionTest {
   }
 
   @Test
-  public void onMediaMetadataChanged_updatesLegacyMetadata_correctModelConversion()
-      throws Exception {
+  public void
+      onMediaMetadataChanged_withGetMetadataAndGetCurrentMediaItemCommand_updatesLegacyMetadata()
+          throws Exception {
     int testItemIndex = 3;
     String testDisplayTitle = "displayTitle";
     long testDurationMs = 30_000;
@@ -1100,6 +1101,12 @@ public class MediaControllerCompatCallbackWithMediaSessionTest {
             .setMediaId(testMediaItems.get(testItemIndex).mediaId)
             .setMediaMetadata(testMediaMetadata)
             .build());
+    session
+        .getMockPlayer()
+        .notifyAvailableCommandsChanged(
+            new Player.Commands.Builder()
+                .addAll(Player.COMMAND_GET_METADATA, Player.COMMAND_GET_CURRENT_MEDIA_ITEM)
+                .build());
     session.getMockPlayer().setTimeline(new PlaylistTimeline(testMediaItems));
     session.getMockPlayer().setCurrentMediaItemIndex(testItemIndex);
     session.getMockPlayer().setDuration(testDurationMs);
@@ -1132,6 +1139,49 @@ public class MediaControllerCompatCallbackWithMediaSessionTest {
   }
 
   @Test
+  public void onMediaMetadataChanged_withGetMetadataCommandOnly_updatesLegacyMetadata()
+      throws Exception {
+    int testItemIndex = 3;
+    String testDisplayTitle = "displayTitle";
+    List<MediaItem> testMediaItems = MediaTestUtils.createMediaItems(/* size= */ 5);
+    MediaMetadata testMediaMetadata =
+        new MediaMetadata.Builder().setTitle(testDisplayTitle).build();
+    testMediaItems.set(
+        testItemIndex,
+        new MediaItem.Builder()
+            .setMediaId(testMediaItems.get(testItemIndex).mediaId)
+            .setMediaMetadata(testMediaMetadata)
+            .build());
+    session
+        .getMockPlayer()
+        .notifyAvailableCommandsChanged(
+            new Player.Commands.Builder().add(Player.COMMAND_GET_METADATA).build());
+    session.getMockPlayer().setTimeline(new PlaylistTimeline(testMediaItems));
+    session.getMockPlayer().setCurrentMediaItemIndex(testItemIndex);
+    AtomicReference<MediaMetadataCompat> metadataRef = new AtomicReference<>();
+    CountDownLatch latchForMetadata = new CountDownLatch(1);
+    MediaControllerCompat.Callback callback =
+        new MediaControllerCompat.Callback() {
+          @Override
+          public void onMetadataChanged(MediaMetadataCompat metadata) {
+            metadataRef.set(metadata);
+            latchForMetadata.countDown();
+          }
+        };
+    controllerCompat.registerCallback(callback, handler);
+
+    session.getMockPlayer().notifyMediaMetadataChanged(testMediaMetadata);
+
+    assertThat(latchForMetadata.await(TIMEOUT_MS, MILLISECONDS)).isTrue();
+    MediaMetadataCompat parameterMetadataCompat = metadataRef.get();
+    MediaMetadataCompat getterMetadataCompat = controllerCompat.getMetadata();
+    assertThat(parameterMetadataCompat.getString(MediaMetadataCompat.METADATA_KEY_DISPLAY_TITLE))
+        .isEqualTo(testDisplayTitle);
+    assertThat(getterMetadataCompat.getString(MediaMetadataCompat.METADATA_KEY_DISPLAY_TITLE))
+        .isEqualTo(testDisplayTitle);
+  }
+
+  @Test
   public void playlistChange() throws Exception {
     AtomicReference<List<QueueItem>> queueRef = new AtomicReference<>();
     CountDownLatch latch = new CountDownLatch(1);