ZOOKEEPER-4033: Remove unnecessary judgment of null

Author: lan <1728209643@qq.com>

Reviewers: Enrico Olivelli <eolivelli@apache.org>, Damien Diederen <ddiederen@apache.org>

Closes #1562 from lanicc/ZOOKEEPER-4033

zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/QuorumPeerMain.java

@@ -150,7 +150,7 @@ public class QuorumPeerMain {
         }
 
         LOG.info("Starting quorum peer, myid=" + config.getServerId());
-        MetricsProvider metricsProvider;
+        final MetricsProvider metricsProvider;
         try {
             metricsProvider = MetricsProviderBootstrap.startMetricsProvider(
                 config.getMetricsProviderClassName(),
@@ -233,12 +233,10 @@ public class QuorumPeerMain {
             // warn, but generally this is ok
             LOG.warn("Quorum Peer interrupted", e);
         } finally {
-            if (metricsProvider != null) {
-                try {
-                    metricsProvider.stop();
-                } catch (Throwable error) {
-                    LOG.warn("Error while stopping metrics", error);
-                }
+            try {
+                metricsProvider.stop();
+            } catch (Throwable error) {
+                LOG.warn("Error while stopping metrics", error);
             }
         }
     }