YARN-6517. Fix warnings from Spotbugs in hadoop-yarn-common. Contributed by Weiwei Yang

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/logaggregation/AggregatedLogFormat.java

@@ -310,6 +310,10 @@ public class AggregatedLogFormat {
     }
 
     private Set<File> getPendingLogFilesToUpload(File containerLogDir) {
+      if(containerLogDir == null ||
+          containerLogDir.listFiles() == null) {
+        return new HashSet<>(0);
+      }
       Set<File> candidates =
           new HashSet<File>(Arrays.asList(containerLogDir.listFiles()));
       for (File logFile : candidates) {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/util/ProcfsBasedProcessTree.java

@@ -481,18 +481,21 @@ public class ProcfsBasedProcessTree extends ResourceCalculatorProcessTree {
    * Get the list of all processes in the system.
    */
   private List<String> getProcessList() {
-    String[] processDirs = (new File(procfsDir)).list();
     List<String> processList = new ArrayList<String>();
-
-    for (String dir : processDirs) {
-      Matcher m = numberPattern.matcher(dir);
-      if (!m.matches()) continue;
-      try {
-        if ((new File(procfsDir, dir)).isDirectory()) {
-          processList.add(dir);
+    String[] processDirs = (new File(procfsDir)).list();
+    if (processDirs != null) {
+      for (String dir : processDirs) {
+        Matcher m = numberPattern.matcher(dir);
+        if (!m.matches()) {
+          continue;
+        }
+        try {
+          if ((new File(procfsDir, dir)).isDirectory()) {
+            processList.add(dir);
+          }
+        } catch (SecurityException s) {
+          // skip this process
         }
-      } catch (SecurityException s) {
-        // skip this process
       }
     }
     return processList;