AJ-943: add exception info check for 'getNewLeader' in AbstractClient;

Author: chengyitian

src/com/xxdb/streaming/client/AbstractClient.java

@@ -1179,6 +1179,10 @@ private DBConnection createSubscribeInternalDBConnection() {
     }
 
     public boolean getNewLeader(String s, Object[] hostPort) {
+        if (Objects.isNull(s)) {
+            return false;
+        }
+
         int index = s.indexOf("<NotLeader>");
         if (index == -1) {
             return false;