diff --git a/UPGRADE-5.0.md b/UPGRADE-5.0.md
index 8b2b5c14d2947..710560b76927a 100644
--- a/UPGRADE-5.0.md
+++ b/UPGRADE-5.0.md
@@ -480,7 +480,7 @@ Serializer
 Stopwatch
 ---------
 
- * Removed support of passing `null` as 1st (`$id`) argument of `Section::get()` method, pass a valid child section identifier instead.
+ * Removed support for passing `null` as 1st (`$id`) argument of `Section::get()` method, pass a valid child section identifier instead.
 
 Translation
 -----------
diff --git a/src/Symfony/Component/HttpKernel/Debug/TraceableEventDispatcher.php b/src/Symfony/Component/HttpKernel/Debug/TraceableEventDispatcher.php
index 6c96afdff3908..ce4ddb35d3f75 100644
--- a/src/Symfony/Component/HttpKernel/Debug/TraceableEventDispatcher.php
+++ b/src/Symfony/Component/HttpKernel/Debug/TraceableEventDispatcher.php
@@ -41,6 +41,9 @@ protected function beforeDispatch(string $eventName, $event)
                 break;
             case KernelEvents::TERMINATE:
                 $token = $event->getResponse()->headers->get('X-Debug-Token');
+                if (null === $token) {
+                    break;
+                }
                 // There is a very special case when using built-in AppCache class as kernel wrapper, in the case
                 // of an ESI request leading to a `stale` response [B]  inside a `fresh` cached response [A].
                 // In this case, `$token` contains the [B] debug token, but the  open `stopwatch` section ID
@@ -65,12 +68,18 @@ protected function afterDispatch(string $eventName, $event)
                 break;
             case KernelEvents::RESPONSE:
                 $token = $event->getResponse()->headers->get('X-Debug-Token');
+                if (null === $token) {
+                    break;
+                }
                 $this->stopwatch->stopSection($token);
                 break;
             case KernelEvents::TERMINATE:
                 // In the special case described in the `preDispatch` method above, the `$token` section
                 // does not exist, then closing it throws an exception which must be caught.
                 $token = $event->getResponse()->headers->get('X-Debug-Token');
+                if (null === $token) {
+                    break;
+                }
                 try {
                     $this->stopwatch->stopSection($token);
                 } catch (\LogicException $e) {
diff --git a/src/Symfony/Component/HttpKernel/Tests/Debug/TraceableEventDispatcherTest.php b/src/Symfony/Component/HttpKernel/Tests/Debug/TraceableEventDispatcherTest.php
index 01cf8e97c72b5..0fa6fcde5114d 100644
--- a/src/Symfony/Component/HttpKernel/Tests/Debug/TraceableEventDispatcherTest.php
+++ b/src/Symfony/Component/HttpKernel/Tests/Debug/TraceableEventDispatcherTest.php
@@ -62,15 +62,13 @@ public function testStopwatchCheckControllerOnRequestEvent()
     public function testStopwatchStopControllerOnRequestEvent()
     {
         $stopwatch = $this->getMockBuilder('Symfony\Component\Stopwatch\Stopwatch')
-            ->setMethods(['isStarted', 'stop', 'stopSection'])
+            ->setMethods(['isStarted', 'stop'])
             ->getMock();
         $stopwatch->expects($this->once())
             ->method('isStarted')
             ->willReturn(true);
         $stopwatch->expects($this->once())
             ->method('stop');
-        $stopwatch->expects($this->once())
-            ->method('stopSection');
 
         $dispatcher = new TraceableEventDispatcher(new EventDispatcher(), $stopwatch);
 
diff --git a/src/Symfony/Component/Stopwatch/CHANGELOG.md b/src/Symfony/Component/Stopwatch/CHANGELOG.md
index 85a62f0181190..14b7dc6dd5ef3 100644
--- a/src/Symfony/Component/Stopwatch/CHANGELOG.md
+++ b/src/Symfony/Component/Stopwatch/CHANGELOG.md
@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+5.0.0
+-----
+
+ * Removed support for passing `null` as 1st (`$id`) argument of `Section::get()` method, pass a valid child section identifier instead.
+
 4.4.0
 -----
 
diff --git a/src/Symfony/Component/Stopwatch/Stopwatch.php b/src/Symfony/Component/Stopwatch/Stopwatch.php
index 19e59bec501f5..9a3fe56d86e78 100644
--- a/src/Symfony/Component/Stopwatch/Stopwatch.php
+++ b/src/Symfony/Component/Stopwatch/Stopwatch.php
@@ -81,7 +81,7 @@ public function openSection(string $id = null)
      *
      * @throws \LogicException When there's no started section to be stopped
      */
-    public function stopSection(?string $id)
+    public function stopSection(string $id)
     {
         $this->stop('__section__');