YARN-3600. AM container link is broken (Naganarasimha G R via tgraves

hadoop-yarn-project/CHANGES.txt

@@ -353,6 +353,8 @@ Release 2.8.0 - UNRELEASED
 
     YARN-3589. RM and AH web UI display DOCTYPE wrongly. (Rohith via ozawa)
 
+    YARN-3600. AM container link is broken (Naganarasimha G R via tgraves)
+
 Release 2.7.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/RMAppAttemptBlock.java

@@ -229,8 +229,9 @@ public class RMAppAttemptBlock extends AppAttemptBlock{
         "AM Container:",
         appAttempt.getAmContainerId() == null || containers == null
             || !hasAMContainer(appAttemptReport.getAMContainerId(), containers)
-            ? "N/A" : root_url("container", appAttempt.getAmContainerId()),
-        String.valueOf(appAttempt.getAmContainerId()))
+            ? null : root_url("container", appAttempt.getAmContainerId()),
+        appAttempt.getAmContainerId() == null ? "N/A" :
+          String.valueOf(appAttempt.getAmContainerId()))
       ._("Node:", node)
       ._(
         "Tracking URL:",