Add missing @Nullable on BlendMode

Match the subclass definition this is overridding

Fixes: 321785629
Test: make
Change-Id: I844f44d59b15596a64000cc1732ba470b0955ae2
diff --git a/graphics/java/android/graphics/BaseRecordingCanvas.java b/graphics/java/android/graphics/BaseRecordingCanvas.java
index d659ddd..4e88b0e 100644
--- a/graphics/java/android/graphics/BaseRecordingCanvas.java
+++ b/graphics/java/android/graphics/BaseRecordingCanvas.java
@@ -607,7 +607,8 @@
     }
 
     @Override
-    public final void drawMesh(@NonNull Mesh mesh, BlendMode blendMode, @NonNull Paint paint) {
+    public final void drawMesh(@NonNull Mesh mesh, @Nullable BlendMode blendMode,
+            @NonNull Paint paint) {
         if (blendMode == null) {
             blendMode = BlendMode.MODULATE;
         }