HDFS-11517. Include missed change in previous commit.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/metrics/DataNodeDiskMetrics.java

@@ -187,6 +187,7 @@ public class DataNodeDiskMetrics {
    */
   @VisibleForTesting
   public void addSlowDiskForTesting(String slowDiskPath) {
-    diskOutliersStats.put(slowDiskPath, ImmutableMap.of());
+    diskOutliersStats.put(slowDiskPath,
+        ImmutableMap.<DiskOutlierDetectionOp, Double>of());
   }
 }