Fixed the static test failures

Author: Indrani Sonawane

app/code/Magento/VaultGraphQl/Model/Resolver/PaymentTokens.php

@@ -24,7 +24,7 @@ class PaymentTokens implements ResolverInterface
     /**
      * Cart types
      */
-    const BASE_CART_TYPES = [
+    private const BASE_CART_TYPES = [
         'VI' => 'Visa',
         'MC' => 'MasterCard',
         'AE' => 'American Express',
@@ -98,7 +98,7 @@ public function resolve(
      */
     private function getCartDetailsInformation(?string $tokenDetails): ?string
     {
-        if (is_null($tokenDetails)) {
+        if ($tokenDetails === null) {
             return $tokenDetails;
         }
 

dev/tests/api-functional/testsuite/Magento/GraphQl/Vault/CustomerPaymentTokensTest.php

@@ -190,7 +190,8 @@ public function testDeletePaymentTokenIfUserIsNotAuthorized()
     public function testDeletePaymentTokenInvalidPublicHash()
     {
         $this->expectException(\Exception::class);
-        $this->expectExceptionMessage('GraphQL response contains errors: Could not find a token using public hash: ksdfk392ks');
+        $this->expectExceptionMessage('GraphQL response contains errors:
+                                       Could not find a token using public hash: ksdfk392ks');
 
         $currentEmail = 'customer@example.com';
         $currentPassword = 'password';