HDFS-10329. Bad initialisation of StringBuffer in RequestHedgingProxyProvider. Contributed by Lin Yiqun.

(cherry picked from commit c6a2430b47692a72c500373d6fc1bce78652675b)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/RequestHedgingProxyProvider.java

@@ -164,7 +164,7 @@ public class RequestHedgingProxyProvider<T> extends
       return successfulProxy;
     }
     Map<String, ProxyInfo<T>> targetProxyInfos = new HashMap<>();
-    StringBuilder combinedInfo = new StringBuilder('[');
+    StringBuilder combinedInfo = new StringBuilder("[");
     for (int i = 0; i < proxies.size(); i++) {
       ProxyInfo<T> pInfo = super.getProxy();
       incrementProxyIndex();