YARN-9857. TestDelegationTokenRenewer throws NPE but tests pass. Contributed by Ahmed Hussein

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/security/TestDelegationTokenRenewer.java

@@ -778,6 +778,7 @@ public class TestDelegationTokenRenewer {
     RMContext mockContext = mock(RMContext.class);
     when(mockContext.getSystemCredentialsForApps()).thenReturn(
         new ConcurrentHashMap<ApplicationId, SystemCredentialsForAppsProto>());
+    when(mockContext.getDispatcher()).thenReturn(dispatcher);
     ClientRMService mockClientRMService = mock(ClientRMService.class);
     when(mockContext.getClientRMService()).thenReturn(mockClientRMService);
     InetSocketAddress sockAddr =
@@ -837,6 +838,7 @@ public class TestDelegationTokenRenewer {
     RMContext mockContext = mock(RMContext.class);
     when(mockContext.getSystemCredentialsForApps()).thenReturn(
         new ConcurrentHashMap<ApplicationId, SystemCredentialsForAppsProto>());
+    when(mockContext.getDispatcher()).thenReturn(dispatcher);
     ClientRMService mockClientRMService = mock(ClientRMService.class);         
     when(mockContext.getClientRMService()).thenReturn(mockClientRMService);    
     InetSocketAddress sockAddr =                                               
@@ -1460,6 +1462,7 @@ public class TestDelegationTokenRenewer {
     RMContext mockContext = mock(RMContext.class);
     when(mockContext.getSystemCredentialsForApps()).thenReturn(
         new ConcurrentHashMap<ApplicationId, SystemCredentialsForAppsProto>());
+    when(mockContext.getDispatcher()).thenReturn(dispatcher);
     ClientRMService mockClientRMService = mock(ClientRMService.class);
     when(mockContext.getClientRMService()).thenReturn(mockClientRMService);
     InetSocketAddress sockAddr =
@@ -1502,6 +1505,7 @@ public class TestDelegationTokenRenewer {
     RMContext mockContext = mock(RMContext.class);
     when(mockContext.getSystemCredentialsForApps()).thenReturn(
         new ConcurrentHashMap<ApplicationId, SystemCredentialsForAppsProto>());
+    when(mockContext.getDispatcher()).thenReturn(dispatcher);
     ClientRMService mockClientRMService = mock(ClientRMService.class);
     when(mockContext.getClientRMService()).thenReturn(mockClientRMService);
     InetSocketAddress sockAddr =