Fix NPE in EntPayRequest#storeMap when brandId is null

weixin-java-pay/src/main/java/com/github/binarywang/wxpay/bean/entpay/EntPayRequest.java

@@ -249,7 +249,9 @@ protected void storeMap(Map<String, String> map) {
     map.put("desc", description);
     map.put("spbill_create_ip", spbillCreateIp);
     map.put("scene", scene);
-    map.put("brand_id", brandId.toString());
+    if (brandId != null) {
+      map.put("brand_id", brandId.toString());
+    }
     map.put("finder_template_id", finderTemplateId);
   }
 }

weixin-java-pay/src/test/java/com/github/binarywang/wxpay/bean/entpay/EntPayRequestTest.java

@@ -2,6 +2,10 @@
 
 import org.testng.annotations.Test;
 
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
 /**
  * .
  *
@@ -14,4 +18,32 @@ public class EntPayRequestTest {
   public void testToString() {
     System.out.println(EntPayRequest.newBuilder().mchId("123").build().toString());
   }
+
+  /**
+   * 测试 brandId 为 null 时，getSignParams() 不抛出 NullPointerException.
+   */
+  @Test
+  public void testGetSignParamsWithNullBrandId() {
+    EntPayRequest request = EntPayRequest.newBuilder()
+      .mchId("123")
+      .amount(100)
+      .brandId(null)
+      .build();
+    Map<String, String> params = request.getSignParams();
+    assertThat(params).doesNotContainKey("brand_id");
+  }
+
+  /**
+   * 测试 brandId 不为 null 时，getSignParams() 正确包含 brand_id.
+   */
+  @Test
+  public void testGetSignParamsWithNonNullBrandId() {
+    EntPayRequest request = EntPayRequest.newBuilder()
+      .mchId("123")
+      .amount(100)
+      .brandId(1234)
+      .build();
+    Map<String, String> params = request.getSignParams();
+    assertThat(params).containsEntry("brand_id", "1234");
+  }
 }