src/core/Session.php
public function remove(string $key)
    {
        if ($this->contains($key)) {
            $res = $_SESSION[$key];
            unset($_SESSION[$key]);
            return $res;
        } else {
            return null;
        }
    }
public function remove(string $key)
    {
        if ($this->contains($key)) {
            $res = $_SESSION[$key];
            unset($_SESSION[$key]);
            return $res;
        } else {
            return null;
        }
    }
It removes the variable of session by passed key.
@param string $key
@return mixed|null The removed variable value.