diff --git a/tests/src/Functional/RequestTest.php b/tests/src/Functional/RequestTest.php
index 40cc9d1..f123313 100644
--- a/tests/src/Functional/RequestTest.php
+++ b/tests/src/Functional/RequestTest.php
@@ -314,8 +314,10 @@ class RequestTest extends BrowserTestBase {
         $this->assertTrue(empty($missing_tags), 'Method ' . $method . ' for ' . $path . ' has invalid tag(s): ' . implode(', ', $missing_tags));
 
         // Ensure all request schemes are defined.
-        $missing_schemas = array_diff($method_schema['schemes'], $decoded_response['schemes']);
-        $this->assertTrue(empty($missing_schemas), 'Method ' . $method . ' for ' . $path . ' has invalid scheme(s): ' . implode(', ', $missing_schemas));
+        if (isset($method_schema['schemes'])) {
+          $missing_schemas = array_diff($method_schema['schemes'], $decoded_response['schemes']);
+          $this->assertTrue(empty($missing_schemas), 'Method ' . $method . ' for ' . $path . ' has invalid scheme(s): ' . implode(', ', $missing_schemas));
+        }
 
         if (isset($method_schema['security'])) {
           foreach ($method_schema['security'] as $security_definitions) {