Why Swagger with Golang is not working in Vercel production?

I have a Golang project, deployed in vercel environment. Everything is working fine but swagger. Swagger implementation is working fine in dev environment but in the production same route doesn't work. I have used gin-swagger, swag, gin-gonic, vercel. Here is the vercel config file:

vercel.json:

{
    "$schema": "https://openapi.vercel.sh/vercel.json",
    "github": {
    "silent": true
    },
    "trailingSlash": false,
    "redirects": [
    {
        "source": "/",
        "destination": "/api",
        "permanent": false
    },
    {
        "source": "/api",
        "destination": "/api/ping",
        "permanent": false
    }
    ],
    "rewrites": [
    {
        "source": "/api/(.*)",
        "destination": "/api/index.go"
    }
    ]
}

Here is the index.go file:

package api

import (
	"net/http"

	_ "WerkenServer/docs"
	"WerkenServer/handler"

	"github.com/gin-gonic/gin"
	swaggerFiles "github.com/swaggo/files"
	ginSwagger "github.com/swaggo/gin-swagger"
)

var (
	app *gin.Engine
)

func registerRouter(r *gin.RouterGroup) {
	r.GET("/ping", handler.Ping)
    r.GET("/doc/*any", ginSwagger.WrapHandler(swaggerFiles.Handler))
	ginSwagger.WrapHandler(swaggerFiles.Handler,
		ginSwagger.URL("https://werken-server.vercel.app/api/doc/doc.json"),
		ginSwagger.DefaultModelsExpandDepth(-1))
}

func init() {
	app = gin.New()

	app.NoRoute(handler.ErrRouter)
	r := app.Group("/api")
	registerRouter(r)
}

// Entrypoint
func Handler(w http.ResponseWriter, r *http.Request) {
	app.ServeHTTP(w, r)
}

I have talked with vercel team and they found an issue in their system. c.Request.RequestURI is returning sometimes empty. They ensured they will solve the issue, and provided me a workaround to unblock. Here is the workaround,

func init() {
	app = gin.New()
	app.GET("/doc/*any", FixRequestUri)
}

func FixRequestUri(c *gin.Context) {
	if c.Request.RequestURI == "" {
		c.Request.RequestURI = c.Request.URL.Path
	}

	ginSwagger.WrapHandler(swaggerFiles.Handler)(c)
}

You can get the full workable example code here: Golang vercel example template