YARN-8129. Improve error message for invalid value in fields attribute. Contributed by Abhishek Modi.

(cherry picked from commit d3fef7a5c5b83d27e87b5e49928254a7d1b935e5)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-timelineservice/src/main/java/org/apache/hadoop/yarn/server/timelineservice/reader/TimelineReaderWebServicesUtils.java

@@ -214,7 +214,11 @@ public final class TimelineReaderWebServicesUtils {
     String[] strs = str.split(delimiter);
     EnumSet<Field> fieldList = EnumSet.noneOf(Field.class);
     for (String s : strs) {
-      fieldList.add(Field.valueOf(s.trim().toUpperCase()));
+      try {
+        fieldList.add(Field.valueOf(s.trim().toUpperCase()));
+      } catch (IllegalArgumentException e) {
+        throw new IllegalArgumentException(s + " is not a valid field.");
+      }
     }
     return fieldList;
   }