diff --git a/src/main/java/com/android/tools/r8/optimize/argumentpropagation/ArgumentPropagatorProgramOptimizer.java b/src/main/java/com/android/tools/r8/optimize/argumentpropagation/ArgumentPropagatorProgramOptimizer.java
index 2a5a4cd..4890dd9 100644
--- a/src/main/java/com/android/tools/r8/optimize/argumentpropagation/ArgumentPropagatorProgramOptimizer.java
+++ b/src/main/java/com/android/tools/r8/optimize/argumentpropagation/ArgumentPropagatorProgramOptimizer.java
@@ -820,7 +820,9 @@
       assert newReturnTypeElement.isTop()
           || newReturnTypeElement.lessThanOrEqual(staticType.toTypeElement(appView), appView);
       if (!newReturnTypeElement.isClassType()) {
-        assert newReturnTypeElement.isArrayType() || newReturnTypeElement.isTop();
+        assert newReturnTypeElement.isArrayType()
+            || newReturnTypeElement.isNullType()
+            || newReturnTypeElement.isTop();
         return null;
       }
       DexType newReturnType = newReturnTypeElement.asClassType().toDexType(dexItemFactory);