Fix NPE in EntPayRequest#storeMap when brandId is null

[Copilot]

EntPayRequest.storeMap() unconditionally called brandId.toString(), but brand_id is an optional field — causing NPE whenever the request was serialized (e.g. via Jackson) without brandId set.

Changes

• EntPayRequest.java: Guard brand_id map insertion with a null check; the key is omitted entirely when brandId is null

  // Before
  map.put("brand_id", brandId.toString());
  
  // After
  if (brandId != null) {
    map.put("brand_id", brandId.toString());
  }

• EntPayRequestTest.java: Add tests covering brandId = null (key absent, no NPE) and brandId set (correct value present)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>com.github.binarywang.wxpay.bean.entpay.EntPayRequest#storeMap中brandId空指针异常</issue_title>
<issue_description>### 简要描述
com.github.binarywang.wxpay.bean.entpay.EntPayRequest#storeMap
brandId非必填但在storeMap中brandId.toString()是否会容易出现空指针异常

模块版本情况

• WxJava 模块名: 微信支付
• WxJava 版本号: v4.8.0

详细描述

在使用sdk企业付款到零钱时，为了方便重试或者为了记录日志，会在每次调用api后保存请求参数与响应参数，使用jackson以json字符串入库但现在因为brandId的问题无法转为json字符串，会报空指针异常

日志

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: com.github.binarywang.wxpay.bean.entpay.EntPayRequest["signParams"])
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:392)
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:351)
at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:316)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:782)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:178)
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480)
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319)
at com.fasterxml.jackson.databind.ObjectMapper._writeValueAndClose(ObjectMapper.java:4568)
at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:3821)
at com.wikemi.huodongbao.framework.common.util.json.JsonUtils.toJsonString(JsonUtils.java:50)
at com.wikemi.huodongbao.app.wx.WxPayTest.main(WxPayTest.java:260)
Caused by: java.lang.NullPointerException
at com.github.binarywang.wxpay.bean.entpay.EntPayRequest.storeMap(EntPayRequest.java:252)
at com.github.binarywang.wxpay.bean.request.BaseWxPayRequest.getSignParams(BaseWxPayRequest.java:329)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:689)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:774)
</issue_description>

Comments on the Issue (you are @copilot in this section)

Custom agent used: 全部用中文
需要用中文，包括PR标题和分析总结过程

• Fixes com.github.binarywang.wxpay.bean.entpay.EntPayRequest#storeMap中brandId空指针异常 #3908

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Pull request overview

该 PR 修复了微信支付“企业付款到零钱”请求对象 EntPayRequest 在序列化/签名参数组装过程中因 brandId（可选字段）为空而触发的空指针异常问题，提升了 SDK 在可选参数未设置时的健壮性（对应 issue #3908 的场景：Jackson 序列化触发 getSignParams()）。

Changes:

• 在 EntPayRequest#storeMap 中为 brandId 增加空值判断，为空时不再写入 brand_id，避免 brandId.toString() NPE
• 新增单测覆盖 brandId = null（不包含 brand_id 且不抛异常）与 brandId 非空（包含正确键值）两种情况

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
weixin-java-pay/src/main/java/com/github/binarywang/wxpay/bean/entpay/EntPayRequest.java	storeMap 中对可选字段 brandId 做 null guard，避免 NPE 并在为空时省略 brand_id
weixin-java-pay/src/test/java/com/github/binarywang/wxpay/bean/entpay/EntPayRequestTest.java	补充 getSignParams() 在 brandId 为空/非空场景下的回归测试

[augmentcode]

🤖 Augment PR Summary

Summary: 修复企业付款请求对象在序列化/取签名参数时因 brandId 为空导致的 NPE。

Changes:

• EntPayRequest#storeMap：仅在 brandId != null 时写入 brand_id 参数，避免对空对象调用 toString()
• 新增单测覆盖 brandId 为空/非空两种场景，验证 getSignParams() 行为（不抛异常且参数符合预期）

Technical Notes: brand_id 为可选字段；为空时省略该键与签名/生成 XML 的过滤逻辑一致，避免 Jackson 作为 Bean 属性访问 signParams 时触发异常。

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