[1256] /src/index.js in multi main

I am using nodejs 8.2 and nuxt 1.0.0-alpha.5 with koa2 . when I run npm run dev it would show this error message but still build success. However , if I run npm run build it would show the same error message then fail.

 ERROR  Failed to compile with 1 errors 
This dependency was not found:
* /Users/123/Desktop/Nodejs/folder/src/index.js in multi main
To install it, you can run: npm install --save /Users/123/Desktop/Nodejs/folder/src/
index.js

I initialized the project at /Users/123/Desktop/Nodejs/folder. I have tried to run my koa server by node ./server/index.js with removing nuxt rendering settings and It works well. I didn't create ./src folder either include any js file in that folder.