Nginx reverse proxy to apache adds a trailing slash at the end

I have an nginx reverse proxy set up like this:

/etc/nginx/sites-available/domain.com

server {
        listen 80;
        listen [::]:80;

        root /var/www/html;
        index index.html index.htm index.nginx-debian.html;

        server_name domain.com www.domain.com;

        location / {
        proxy_pass http://localhost:8090;
        autoindex on;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
        }

}

The site is on Apache, which is listening on port 8090.

So, /etc/apache2/ports.conf looks like this:

Listen 8090

<IfModule ssl_module>
        Listen 443
</IfModule>

<IfModule mod_gnutls.c>
        Listen 443
</IfModule>

It works, but a trailing slash is added. So I can see my website at domain.com//

I’m not sure if it’s nginx or apache causing the trailing extra slash at the end. How can I fix this?