I found an error like expressValidator is not a function

I found an error like expressValidator is not a function

Here, It's my code.
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var express = require('express');
var path = require('path');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var hbs = require('express-handlebars');
var expressValidator = require('express-validator');
var expressSession = require('express-session');

var routes = require('./routes/index');

var app = express();

// view engine setup
app.engine('hbs', hbs({extname: 'hbs', defaultLayout: 'layouts', layoutsDir: __dirname + '/views/layouts/'}));
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'hbs');

// uncomment after placing your favicon in /public
//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(expressValidator());
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
app.use(expressSession({secret: 'max', saveUninitialized: false, resave: false}));

app.use('/', routes);

// catch 404 and forward to error handler
app.use(function(req, res, next) {
next(createError(404));
});

// error handler
app.use(function(err, req, res, next) {
// set locals, only providing error in development
res.locals.message = err.message;
res.locals.error = req.app.get('env') === 'development' ? err : {};

// render the error page
res.status(err.status || 500);
res.render('error');
});

module.exports = app;