fix tinkerpop test open graph panic and other bugs

Author: Pengzna

hugegraph-pd/hg-pd-client/src/main/java/org/apache/hugegraph/pd/client/PDConfig.java

@@ -101,6 +101,10 @@ public String toString() {
     }
 
     public PDConfig setAuthority(String userName, String pwd) {
+        // If userName is null or empty, keep default values for test environment
+        if (StringUtils.isEmpty(userName)) {
+            return this;
+        }
         this.userName = userName;
         String auth = userName + ':' + pwd;
         this.authority = Base64.getEncoder().encodeToString(auth.getBytes(UTF_8));

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/io/HugeGraphSONModule.java

@@ -87,7 +87,7 @@ public class HugeGraphSONModule extends TinkerPopJacksonModule {
 
     private static final String TYPE_NAMESPACE = "hugegraph";
 
-    private static final boolean OPTIMIZE_SERIALIZE = true;
+    private static boolean OPTIMIZE_SERIALIZE = true;
 
     @SuppressWarnings("rawtypes")
     private static final Map<Class, String> TYPE_DEFINITIONS;