[fixed] getRelFilePath 返回null 导致KkFileUtils.isAllowedUpload的空指针异常

server/src/main/java/cn/keking/utils/DownloadUtils.java

@@ -49,7 +49,7 @@ public class DownloadUtils {
         }
         ReturnResponse<String> response = new ReturnResponse<>(0, "下载成功!!!", "");
         String realPath = getRelFilePath(fileName, fileAttribute);
-        if (!KkFileUtils.isAllowedUpload(realPath)) {
+        if (null == realPath || !KkFileUtils.isAllowedUpload(realPath)) {
             response.setCode(1);
             response.setContent(null);
             response.setMsg("下载失败:不支持的类型!" + urlStr);