HADOOP-13288. Guard null stats key in FileSystemStorageStatistics (Mingliang Liu via Colin P. McCabe)

(cherry picked from commit 8c1f81d4bf424bdc421cf4952b230344e39a7b68)
(cherry picked from commit 14df17383c20cebcdb27da1f8bce0b494d47b392)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileSystemStorageStatistics.java

@@ -20,6 +20,7 @@ package org.apache.hadoop.fs;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 
+import com.google.common.base.Preconditions;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.fs.FileSystem.Statistics.StatisticsData;
@@ -77,6 +78,9 @@ public class FileSystemStorageStatistics extends StorageStatistics {
   }
 
   private static Long fetch(StatisticsData data, String key) {
+    Preconditions.checkArgument(key != null,
+        "The stat key of FileSystemStorageStatistics should not be null!");
+
     switch (key) {
     case "bytesRead":
       return data.getBytesRead();
@@ -95,6 +99,10 @@ public class FileSystemStorageStatistics extends StorageStatistics {
 
   FileSystemStorageStatistics(String name, FileSystem.Statistics stats) {
     super(name);
+    Preconditions.checkArgument(stats != null,
+        "FileSystem.Statistics can not be null");
+    Preconditions.checkArgument(stats.getData() != null,
+        "FileSystem.Statistics can not have null data");
     this.stats = stats;
   }