Address Error prone warning: [MixedMutabilityReturnType]

Bug: b/353452237
Change-Id: Ibf401bc9b4c137b240064430a3ae7ae47d565ac5
diff --git a/src/main/java/com/android/tools/r8/dex/ApplicationWriterExperimental.java b/src/main/java/com/android/tools/r8/dex/ApplicationWriterExperimental.java
index 99feade..8aaa278 100644
--- a/src/main/java/com/android/tools/r8/dex/ApplicationWriterExperimental.java
+++ b/src/main/java/com/android/tools/r8/dex/ApplicationWriterExperimental.java
@@ -23,7 +23,6 @@
 import com.android.tools.r8.utils.ThreadUtils;
 import com.android.tools.r8.utils.Timing;
 import com.android.tools.r8.utils.Timing.TimingMerger;
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Sets;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -44,7 +43,7 @@
       List<LazyDexString> lazyDexStrings)
       throws ExecutionException {
     if (virtualFiles.size() == 0) {
-      return ImmutableList.of();
+      return new ArrayList<>();
     }
     // Collect strings from all virtual files into the last DEX section.
     VirtualFile lastFile = virtualFiles.get(virtualFiles.size() - 1);