Messaging: Nullability

Change-Id: I8bcde2a868a9c8989971d056be24ff4986e4f8f3

src/com/android/messaging/ui/mediapicker/camerafocus/RenderOverlay.java

@@ -24,6 +24,8 @@ import android.view.MotionEvent;
 import android.view.View;
 import android.widget.FrameLayout;
 
+import androidx.annotation.NonNull;
+
 import java.util.ArrayList;
 import java.util.List;
 
@@ -160,7 +162,7 @@ public class RenderOverlay extends FrameLayout {
         }
 
         @Override
-        public void draw(Canvas canvas) {
+        public void draw(@NonNull Canvas canvas) {
             super.draw(canvas);
             if (mClients == null) {
                 return;