fix fallback to the default model when no router configuration is provided

README.md

@@ -244,3 +244,4 @@ Thanks to the following sponsors for supporting the continued development of thi
 @\*划 (可通过主页邮箱联系我修改 github 用户名)     
 [@Clarence-pan](https://github.com/Clarence-pan)     
 [@carter003](https://github.com/carter003)      
+@S\*r (可通过主页邮箱联系我修改 github 用户名) 

src/utils/router.ts

@@ -9,19 +9,19 @@ const getUseModel = (req: any, tokenCount: number, config: any) => {
     return req.body.model;
   }
   // if tokenCount is greater than 60K, use the long context model
-  if (tokenCount > 1000 * 60) {
+  if (tokenCount > 1000 * 60 && config.Router.longContext) {
     log("Using long context model due to token count:", tokenCount);
-    return config.Router!.longContext;
+    return config.Router.longContext;
   }
   // If the model is claude-3-5-haiku, use the background model
-  if (req.body.model?.startsWith("claude-3-5-haiku")) {
+  if (req.body.model?.startsWith("claude-3-5-haiku") && config.Router.background) {
     log("Using background model for ", req.body.model);
-    return config.Router!.background;
+    return config.Router.background;
   }
   // if exits thinking, use the think model
-  if (req.body.thinking) {
+  if (req.body.thinking && config.Router.think) {
     log("Using think model for ", req.body.thinking);
-    return config.Router!.think;
+    return config.Router.think;
   }
   return config.Router!.default;
 };