src/Checkout/Step/CheckoutStep.php
private function nextstep()
    {
        $steps = $this->owner->getSteps();
        $found = false;
        foreach ($steps as $step => $class) {
            //determine if this is the current step
            if (method_exists($this, $step)) {
                $found = true;
            } elseif ($found) {
                return $step;
            }
        }
        return null;
    }
private function nextstep()
    {
        $steps = $this->owner->getSteps();
        $found = false;
        foreach ($steps as $step => $class) {
            //determine if this is the current step
            if (method_exists($this, $step)) {
                $found = true;
            } elseif ($found) {
                return $step;
            }
        }
        return null;
    }
Get the next step action

@return string|NULL