Check for main dex rules being empty when dumping

Change-Id: I444bb725dd4183c5c7f64b7b9e770fc6984d575e
diff --git a/src/main/java/com/android/tools/r8/DumpOptions.java b/src/main/java/com/android/tools/r8/DumpOptions.java
index 3feeee3..f923ffa 100644
--- a/src/main/java/com/android/tools/r8/DumpOptions.java
+++ b/src/main/java/com/android/tools/r8/DumpOptions.java
@@ -143,7 +143,7 @@
   }
 
   public boolean hasMainDexKeepRules() {
-    return mainDexKeepRules != null;
+    return mainDexKeepRules != null && !mainDexKeepRules.isEmpty();
   }
 
   public List<ProguardConfigurationRule> getMainDexKeepRules() {