fix(cache): 解决缓存中JSON null值导致的空指针问题

- 添加对历史缓存中JSON "null" 字符串的兼容处理
- 当缓存解析出null值时清理缓存并回源数据库
- 在CmsWebsiteServiceImpl中增加缓存清理逻辑
- 在ShopWebsiteServiceImpl中统一缓存异常处理机制
- 添加单元测试验证JSON null值场景的正确回退行为

src/test/java/com/gxwebsoft/cms/service/impl/CmsWebsiteServiceImplCacheTest.java

@@ -0,0 +1,66 @@
+package com.gxwebsoft.cms.service.impl;
+
+import com.gxwebsoft.cms.entity.CmsWebsite;
+import com.gxwebsoft.cms.mapper.CmsWebsiteMapper;
+import com.gxwebsoft.cms.service.CmsNavigationService;
+import com.gxwebsoft.common.core.utils.RedisUtil;
+import com.gxwebsoft.shop.vo.ShopVo;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Field;
+import java.util.Collections;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+class CmsWebsiteServiceImplCacheTest {
+
+    @Test
+    void getSiteInfo_cacheValueIsJsonNull_shouldFallbackToDb() throws Exception {
+        Integer tenantId = 1;
+
+        RedisUtil redisUtil = mock(RedisUtil.class);
+        CmsNavigationService cmsNavigationService = mock(CmsNavigationService.class);
+        CmsWebsiteMapper cmsWebsiteMapper = mock(CmsWebsiteMapper.class);
+
+        // 历史缓存可能存在字符串 "null"；Jackson 解析后会得到 null，需回源 DB。
+        when(redisUtil.get("SiteInfo:" + tenantId)).thenReturn("null");
+        when(cmsNavigationService.listRel(any())).thenReturn(Collections.emptyList());
+
+        CmsWebsite website = new CmsWebsite();
+        website.setTenantId(tenantId);
+        website.setTenantName("tenant");
+        website.setWebsiteName("site");
+        when(cmsWebsiteMapper.getByTenantId(tenantId)).thenReturn(website);
+
+        CmsWebsiteServiceImpl service = new CmsWebsiteServiceImpl();
+        setField(service, "redisUtil", redisUtil);
+        setField(service, "cmsNavigationService", cmsNavigationService);
+        setField(service, "baseMapper", cmsWebsiteMapper);
+
+        ShopVo vo = service.getSiteInfo(tenantId);
+
+        assertNotNull(vo);
+        verify(redisUtil).delete("SiteInfo:" + tenantId);
+        verify(cmsWebsiteMapper).getByTenantId(tenantId);
+    }
+
+    private static void setField(Object target, String fieldName, Object value) throws Exception {
+        Class<?> c = target.getClass();
+        while (c != null) {
+            try {
+                Field f = c.getDeclaredField(fieldName);
+                f.setAccessible(true);
+                f.set(target, value);
+                return;
+            } catch (NoSuchFieldException ignored) {
+                c = c.getSuperclass();
+            }
+        }
+        throw new NoSuchFieldException(fieldName);
+    }
+}
+