Remove build warning (SafeVarArgs)

Change-Id: I46b236b9fd6649dc3048a35d8201bc1ba31cfd4b
diff --git a/src/main/java/com/android/tools/r8/utils/SetUtils.java b/src/main/java/com/android/tools/r8/utils/SetUtils.java
index 0a53f60..a7305a2 100644
--- a/src/main/java/com/android/tools/r8/utils/SetUtils.java
+++ b/src/main/java/com/android/tools/r8/utils/SetUtils.java
@@ -89,6 +89,7 @@
     return builder.build();
   }
 
+  @SafeVarargs
   public static <T> ImmutableSet<T> newImmutableSetExcludingNullItems(T... items) {
     ImmutableSet.Builder<T> builder = ImmutableSet.builder();
     for (T item : items) {