ZOOKEEPER-4853: Fix assert in ZooKeeperQuotaTest#testQuota

Reviewers: maoling, shoothzj
Author: 1neverknow
Closes #2169 from 1neverknow/master

zookeeper-server/src/test/java/org/apache/zookeeper/test/ZooKeeperQuotaTest.java

@@ -116,7 +116,7 @@ public class ZooKeeperQuotaTest extends ClientBase {
         stopServer();
         startServer();
         ZooKeeperServer server = serverFactory.getZooKeeperServer();
-        assertNotNull(server.getZKDatabase().getDataTree().getMaxPrefixWithQuota(path) != null, "Quota is still set");
+        assertNotNull(server.getZKDatabase().getDataTree().getMaxPrefixWithQuota(path), "Quota is still set");
     }
 
     @Test