HADOOP-18074 - clean up of unnecessary null variable

Author: lmccay

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/LdapGroupsMapping.java

@@ -512,6 +512,7 @@ List<String> lookupGroup(SearchResult result, DirContext c,
   List<String> doGetGroups(String user, int goUpHierarchy)
       throws NamingException {
     DirContext c = getDirContext();
+    List<String> groups = new ArrayList<>();
 
     // Search for the user. We'll only ever need to look at the first result
     NamingEnumeration<SearchResult> results = c.search(userbaseDN,
@@ -520,11 +521,10 @@ List<String> doGetGroups(String user, int goUpHierarchy)
     if (!results.hasMoreElements()) {
       LOG.debug("doGetGroups({}) returned no groups because the " +
           "user is not found.", user);
-      return new ArrayList<>();
+      return groups;
     }
     SearchResult result = results.nextElement();
 
-    List<String> groups = null;
     if (useOneQuery) {
       try {
         /**
@@ -538,7 +538,6 @@ List<String> doGetGroups(String user, int goUpHierarchy)
               memberOfAttr + "' attribute." +
               "Returned user object: " + result.toString());
         }
-        groups = new ArrayList<>();
         NamingEnumeration groupEnumeration = groupDNAttr.getAll();
         while (groupEnumeration.hasMore()) {
           String groupDN = groupEnumeration.next().toString();
@@ -547,14 +546,12 @@ List<String> doGetGroups(String user, int goUpHierarchy)
       } catch (NamingException e) {
         // If the first lookup failed, fall back to the typical scenario.
         // In order to force the fallback, we need to reset groups collection.
-        if (groups != null) {
-          groups.clear();
-        }
+        groups.clear();
         LOG.info("Failed to get groups from the first lookup. Initiating " +
                 "the second LDAP query using the user's DN.", e);
       }
     }
-    if (groups == null || groups.isEmpty() || goUpHierarchy > 0) {
+    if (groups.isEmpty() || goUpHierarchy > 0) {
       groups = lookupGroup(result, c, goUpHierarchy);
     }
     LOG.debug("doGetGroups({}) returned {}", user, groups);