Fix NPE in IfRuleEvaluatorFactory

Change-Id: If90aa15234bb1d49fc2cf7ff3fe7da71819f5469

src/main/java/com/android/tools/r8/shaking/IfRuleEvaluatorFactory.java

diff --git a/src/main/java/com/android/tools/r8/shaking/IfRuleEvaluatorFactory.java b/src/main/java/com/android/tools/r8/shaking/IfRuleEvaluatorFactory.java
index dc438f3..1f316e2 100644
--- a/src/main/java/com/android/tools/r8/shaking/IfRuleEvaluatorFactory.java
+++ b/src/main/java/com/android/tools/r8/shaking/IfRuleEvaluatorFactory.java
@@ -53,7 +53,8 @@
       AppView<? extends AppInfoWithClassHierarchy> appView,
       Enqueuer enqueuer,
       ExecutorService executorService) {
-    Set<ProguardIfRule> ifRules = appView.rootSet().ifRules;
+    Set<ProguardIfRule> ifRules =
+        appView.hasRootSet() ? appView.rootSet().ifRules : Collections.emptySet();
     if (ifRules != null && !ifRules.isEmpty()) {
       enqueuer.registerAnalysis(new IfRuleEvaluatorFactory(appView, enqueuer, executorService));
     }