修复未使用pay-java-web-support组件的回调对象时json序列化空指针异常bug

pay-java-common/src/main/java/com/egzosn/pay/common/api/BasePayService.java

@@ -350,7 +350,7 @@ public abstract class BasePayService<PC extends PayConfigStorage> implements Pay
      */
     @Override
     public Map<String, Object> transfer(TransferOrder order) {
-        return new HashMap<>(0);
+        return Collections.emptyMap();
     }
 
     /**
@@ -362,7 +362,7 @@ public abstract class BasePayService<PC extends PayConfigStorage> implements Pay
      */
     @Override
     public Map<String, Object> transferQuery(String outNo, String tradeNo) {
-        return new HashMap<>(0);
+        return Collections.emptyMap();
     }
 
     /**

pay-java-common/src/main/java/com/egzosn/pay/common/bean/NoticeParams.java

@@ -70,6 +70,9 @@ public class NoticeParams {
     }
 
     public Enumeration<String> getHeaderNames() {
+        if (null == headers){
+            return  Collections.enumeration(Collections.emptySet());
+        }
         return Collections.enumeration(this.headers.keySet());
     }