Error is undefinne headersent

const express = require(‘express’)
const Router = express()
const route = Router()

const student = [
{name:“Aditya”,college:“Ignou”,year:3},
{name:“Rishab”,college:“JIMS”,year:1},
{name:“Faizan”,college:“VIPS”,year:2},
{name:“Aditya Prasher”,college:“Ignou”,year:3},

]
route.get(’/’,(req,res)=> res.send(student))
route.get(’/:id’,(req,res)=> res.send(student[req.params.id]))
module.exports = route

// server file coding
const express = require(‘express’)
const server = express();

const objstudent = require("./routes/student")
const objteacher = require(’./routes/teacher’)

server.use(’/teacher’,objteacher)
server.use(’/student’,objstudent)
server.listen(1112,()=> console.log(“SERVER RUN IN PORT NO:1112”))

// teacher file coding
/* Make a router
const express = require(‘express’)
const Router = express.Router();
const router = Router();

*/

// Make a router in short
const route = express(‘express’).Router();

const teachers = [
{name:“Arnav”,Sub:“WEb DEvelopment”},
{name:“Parteek”,Sub:“Competititve”}

]

route.get(’/’,(req,res)=>res.send(teachers))
//its work client side when user add new objects and it not work when page refresh
/*
route.get(’/add’,(req,res)=>{
teachers.push({
name:req.query.name,
Sub:req.query.Sub
})
})
*/
route.get(’/:id’,(req,res)=>res.send(teachers[req.params.id]))
module.exports = route