我想只在用户登录时在导航栏中显示“注销”选项，或者只在导航栏中显示主页、登录和注册选项。但它显示了标题中提到的错误
在应用控制器. php中

public function beforeRender(EventInterface $event)
  {
    if (is_object($this->Authentication)) {
        if ($this->Authentication->user() !== null) {
            $this->set("userIsLoggedIn", true);

        } else {
            $this->set("userIsLoggedIn", false);

        }
    }
  }

在nav.php文件中

<?php if(isset($userIsLoggedIn) && $userIsLoggedIn): ?>
        <li class="nav-item">
            <?= $this->Html->link(
                'Logout',
                '/users/logout',
                ['class' => 'nav-link','target' => '_self']
            ); ?>
        </li>
 <?php else: ?>
        <li class="nav-item">
            <?= $this->Html->link(
                'Login',
                '/users/login',
                ['class' => 'nav-link','target' => '_self']
            ); ?>
        </li>

        <li class="nav-item">
            <?= $this->Html->link(
                'Signup',
                '/users/signup',
                ['class' => 'nav-link','target' => '_self']
            ); ?>
        </li>
  <?php endif; ?>