ReferenceError: usuario is not defined

Question

I'm trying to do some validation, but ReferenceError appears when I run the code.

The errror:

C:\Users\User\Desktop\Login-node-mvc-mysql\lOGIN-REGISTER\controllers\UserController.js:21
    if (!usuario) {
    ^

ReferenceError: usuario is not defined

Front:

<h2>Faça seu registro</h2>

<form action="/users/register" method="POST">
  <div class="form-control">
    <label for="title">Usuário:</label>
    <input type="text" name="usuario" placeholder="nome de usuario">
  </div>
  <div class="form-control">
    <label for="description">Senha:</label>
    <input type="password" name="senha" placeholder="sua senha"></input>
  </div>
  <div class="form-control">
    <label for="description">Confirmar Senha:</label>
    <input type="password" name="confirmarsenha" placeholder="Repita sua senha"></input>
  </div>
  <input type="submit" value="Registar">
</form>

Controller:

module.exports = class UserController {
  
  // CADASTRO DE USUARIO //
  static register(req, res) {
    res.render('users/register')
  }

  static async registerSave(req, res){

    const user = {
      usuario: req.body.usuario,
      senha: req.body.senha,
      confirmarsenha: req.body.confirmarsenha,
    }


    if (!usuario) {
      res.send('Usuario é obrigatorio')
      return
    } 
    
   
    await User.create(user)

    res.redirect('/users/login')
  }

  static login(req, res){
    res.render('users/login')
  }
}

I try change the name, but the error persists.