feat：修改代码

lib/core/services/version_service/impl/pm_version_impl.dart

@@ -18,8 +18,10 @@ class PMVersionImpl implements VersionService {
   Future<VersionInfo?> checkVersion() async {
     // ①版本检测
     var checkResult = await checkVersionPM();
+    if (checkResult == null) return null;
     // ②获取版本详情
     var result = await getVersionDetailPM(checkResult?['id']);
+    if (result == null) return null;
     // 返回升级版本信息
     return VersionInfo(
       name: result['name'],