Call to a member function login() on null

<?php

declare(strict_types=1);

namespace FrontModule;

use Nette;
use App\Model;
use Nette\Application\UI;
use Nette\Mail\Message;
use Nette\Mail\SendmailMailer;
use Nette\Application\UI\Form;
use Nette\Security\Passwords;
use Nette\Security\User;

abstract class BasePresenter extends Nette\Application\UI\Presenter
{
	/** @var \Nette\Security\User @inject */
	private $user;

  /** @persistent */
  public $backlink = '';

	/** @var \Nette\Database\Context @inject */
  private $database;

	/** @var Model\UserManager */
	private $userManager;

	/** @var Passwords */
	private $passwords;

	public function __construct(Nette\Database\Context $database, User $user, Model\UserManager $userManager, Passwords $passwords) {
    $this->database = $database;
		$this->userManager = $userManager;
		$this->passwords = $passwords;
		$this->user = $user;
  }

  protected function createComponentSignInForm()
  {
    $form = new Form;
		$form->getElementPrototype()->class('ajax');

		$form->addText('email', 'Uživatel:')
			->setRequired('Zadejte prosím přihlašovací údaje')
			->setAttribute('placeholder', 'Uživatelské jméno');

		$form->addPassword('password', 'Heslo:')
			->setRequired('Zadejte prosím přihlašovací údaje')
			->setAttribute('placeholder', 'Heslo');

		$form->addSubmit('send', 'Přihlásit')->setAttribute('class', 'primary-big-button');

    $form->onSuccess[] = [$this, 'signInFormSucceeded'];
    $form->onError[] = function (Form $form) {
        if ($this->presenter->isAjax()) {
					$this->redrawControl('sign_in_form');
        }
    };
    return $form;
  }

	public function signInFormSucceeded(UI\Form $form, $values)
  {
		try {
			$this->user->login($values["email"], $values["password"]);
			$this->redirect('Homepage:default');
		} catch (Nette\Security\AuthenticationException $e) {
			$form->addError('E-mail nebo heslo je chybné.');
			return;
		}
	}
}