YARN-10829. Follow up: Adding null checks before merging ResourceUsage Report (#3252)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/main/java/org/apache/hadoop/yarn/server/router/clientrm/RouterYarnClientUtils.java

@@ -133,6 +133,10 @@ public final class RouterYarnClientUtils {
     ApplicationResourceUsageReport uamResourceReport =
         uam.getApplicationResourceUsageReport();
 
+    if (amResourceReport == null) {
+      am.setApplicationResourceUsageReport(uamResourceReport);
+    } else if (uamResourceReport != null) {
+
       amResourceReport.setNumUsedContainers(
           amResourceReport.getNumUsedContainers() +
               uamResourceReport.getNumUsedContainers());
@@ -171,6 +175,7 @@ public final class RouterYarnClientUtils {
 
       am.setApplicationResourceUsageReport(amResourceReport);
     }
+  }
 
   /**
    * Returns whether or not to add an unmanaged application to the report.

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/test/java/org/apache/hadoop/yarn/server/router/clientrm/TestRouterYarnClientUtils.java

@@ -124,6 +124,48 @@ public class TestRouterYarnClientUtils {
     Assert.assertTrue(result.getApplicationList().isEmpty());
   }
 
+  /**
+   * This test validates the correctness of
+   * RouterYarnClientUtils#mergeApplications when
+   * ApplicationResourceUsageReport might be null.
+   */
+  @Test
+  public void testMergeApplicationsNullResourceUsage() {
+    ApplicationId appId = ApplicationId.newInstance(1234, 1);
+    ApplicationReport appReport = ApplicationReport.newInstance(
+        appId, ApplicationAttemptId.newInstance(appId, 1),
+        "user", "queue", "app1", "host",
+        124, null, YarnApplicationState.RUNNING,
+        "diagnostics", "url", 0, 0,
+        0, FinalApplicationStatus.SUCCEEDED, null, "N/A",
+        0.53789f, "YARN", null, null, false, null, null, null);
+
+    ApplicationReport uamAppReport = ApplicationReport.newInstance(
+        appId, ApplicationAttemptId.newInstance(appId, 1),
+        "user", "queue", "app1", "host",
+        124, null, YarnApplicationState.RUNNING,
+        "diagnostics", "url", 0, 0,
+        0, FinalApplicationStatus.SUCCEEDED, null, "N/A",
+        0.53789f, "YARN", null, null, true, null, null, null);
+
+
+    ArrayList<GetApplicationsResponse> responses = new ArrayList<>();
+    List<ApplicationReport> applications = new ArrayList<>();
+    applications.add(appReport);
+    applications.add(uamAppReport);
+    responses.add(GetApplicationsResponse.newInstance(applications));
+
+    GetApplicationsResponse result = RouterYarnClientUtils.
+        mergeApplications(responses, false);
+    Assert.assertNotNull(result);
+    Assert.assertEquals(1, result.getApplicationList().size());
+
+    String appName = result.getApplicationList().get(0).getName();
+
+    // Check that no Unmanaged applications are added to the result
+    Assert.assertFalse(appName.contains(UnmanagedApplicationManager.APP_NAME));
+  }
+
   /**
    * This generates a GetApplicationsResponse with 2 applications with
    * same ApplicationId.