Issue #3270758 by abramm: Introduce strict interface check

src/PluginForm/Omise/PaymentMethodAddForm.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\commerce_omise\PluginForm\Omise;
 
+use Drupal\commerce_omise\Plugin\Commerce\PaymentGateway\OmiseInterface;
 use Drupal\commerce_payment\PluginForm\PaymentMethodAddForm as BasePaymentMethodAddForm;
 use Drupal\Core\Form\FormStateInterface;
 
@@ -22,10 +23,11 @@ class PaymentMethodAddForm extends BasePaymentMethodAddForm {
     $element['#attributes']['class'][] = 'omise-form';
 
     // Set our key to settings array.
-    /** @var \Drupal\commerce_omise\Plugin\Commerce\PaymentGateway\OmiseInterface $plugin */
-    $plugin = $this->plugin;
+    if (!($this->plugin instanceof OmiseInterface)) {
+      throw new \InvalidArgumentException('Omise payment method required.');
+    }
     $element['#attached']['drupalSettings']['commerceOmise'] = [
-      'publicKey' => $plugin->getPublicKey(),
+      'publicKey' => $this->plugin->getPublicKey(),
     ];
 
     // To display validation errors.