微信V3版本接入直连接口，自测通过

pay-java-common/src/main/java/com/egzosn/pay/common/util/MapGen.java

@@ -1,5 +1,7 @@
 package com.egzosn.pay.common.util;
 
+import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.Map;
 
 /**
@@ -21,6 +23,9 @@ public class MapGen<K, V> {
     }
 
     public MapGen<K, V> keyValue(K key, V value) {
+        if (null == attr){
+            attr = new LinkedHashMap<>();
+        }
         attr.put(key, value);
         return this;
     }

pay-java-common/src/main/java/com/egzosn/pay/common/util/str/StringUtils.java

@@ -153,7 +153,7 @@ public class StringUtils {
     public static String joining(String separator, String... str) {
         StringBuilder builder = new StringBuilder();
         for (String s : str) {
-            if (StringUtils.isEmpty(s)) {
+            if (null == s) {
                 continue;
             }