How to understand if parameter is empty

Hi. For example i have a delete method in users controller. I want to if there is no parameter i should redirect the user.

For example these codes are not working. I am waiting advices.

PHP Code:

public function delete($incomingId)
    {
        if (empty($incomingId)) {
            redirect(base_url());
        }
    } 


or

PHP Code:

public function delete($incomingId)
    {
        if (!$incomingId) {
            redirect(base_url());
        }
    } 


PHP Code:

public function delete($incomingId)
    {
        if (!isset($incomingId)) {
            redirect(base_url());
        }
    }