diff --git a/tests/src/Functional/ResourceTestBase.php b/tests/src/Functional/ResourceTestBase.php
index c949382..08561a1 100644
--- a/tests/src/Functional/ResourceTestBase.php
+++ b/tests/src/Functional/ResourceTestBase.php
@@ -429,7 +429,7 @@ abstract class ResourceTestBase extends BrowserTestBase {
    * @param int $expected_status_code
    *   The expected response status.
    * @param array|null|false $expected_document
-   *   The expected document or NULL if there should be not be a response body.
+   *   The expected document or NULL if there should not be a response body.
    *   FALSE in case this should not be asserted.
    * @param \Psr\Http\Message\ResponseInterface $response
    *   The response to assert.
@@ -464,7 +464,7 @@ abstract class ResourceTestBase extends BrowserTestBase {
       if ($expected_document !== FALSE) {
         $response_document = Json::decode((string) $response->getBody());
         if ($expected_document === NULL) {
-          $this->assertTrue(is_null($response_document));
+          $this->assertNull($response_document);
         }
         else {
           $this->assertSameDocument($expected_document, $response_document);