fix: 处理 YAML short-id 为 null 的情况

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "sub-store",
-  "version": "2.18.3",
+  "version": "2.18.4",
   "description": "Advanced Subscription Manager for QX, Loon, Surge, Stash and Shadowrocket.",
   "main": "src/main.js",
   "scripts": {

backend/src/core/proxy-utils/preprocessors/index.js

@@ -75,6 +75,8 @@ function Clash() {
                 // 是否被引号包裹
                 if (/^(['"]).*\1$/.test(afterTrim)) {
                     return `short-id: ${afterTrim}`;
+                } else if (['null'].includes(afterTrim)) {
+                    return `short-id: ${afterTrim}`;
                 } else {
                     return `short-id: "${afterTrim}"`;
                 }