diff --git a/src/Symfony/Bridge/Monolog/Handler/FirePHPHandler.php b/src/Symfony/Bridge/Monolog/Handler/FirePHPHandler.php
index 056496ae13..966a7baf83 100644
--- a/src/Symfony/Bridge/Monolog/Handler/FirePHPHandler.php
+++ b/src/Symfony/Bridge/Monolog/Handler/FirePHPHandler.php
@@ -38,9 +38,10 @@ class FirePHPHandler extends BaseFirePHPHandler
             return;
         }
 
-        if (!preg_match('{\bFirePHP/\d+\.\d+\b}', $event->getRequest()->headers->get('User-Agent'))
-            && !$event->getRequest()->headers->has('X-FirePHP-Version')) {
-            $this->sendHeaders = false;
+        $request = $event->getRequest();
+        if (!preg_match('{\bFirePHP/\d+\.\d+\b}', $request->headers->get('User-Agent'))
+            && !$request->headers->has('X-FirePHP-Version')) {
+            self::$sendHeaders = false;
             $this->headers = array();
 
             return;
@@ -58,7 +59,7 @@ class FirePHPHandler extends BaseFirePHPHandler
      */
     protected function sendHeader($header, $content)
     {
-        if (!$this->sendHeaders) {
+        if (!self::$sendHeaders) {
             return;
         }
 
diff --git a/src/Symfony/Bundle/WebProfilerBundle/Resources/views/Profiler/toolbar.css.twig b/src/Symfony/Bundle/WebProfilerBundle/Resources/views/Profiler/toolbar.css.twig
index 33ca8b4fb2..09056e1770 100644
--- a/src/Symfony/Bundle/WebProfilerBundle/Resources/views/Profiler/toolbar.css.twig
+++ b/src/Symfony/Bundle/WebProfilerBundle/Resources/views/Profiler/toolbar.css.twig
@@ -70,6 +70,7 @@
 .sf-toolbarreset svg,
 .sf-toolbarreset img {
     height: 20px;
+    width: 20px;
     display: inline-block;
 }
 
diff --git a/src/Symfony/Component/HttpKernel/Event/GetResponseEvent.php b/src/Symfony/Component/HttpKernel/Event/GetResponseEvent.php
index f7745ea3dc..c25a0f1cf1 100644
--- a/src/Symfony/Component/HttpKernel/Event/GetResponseEvent.php
+++ b/src/Symfony/Component/HttpKernel/Event/GetResponseEvent.php
@@ -29,7 +29,7 @@ class GetResponseEvent extends KernelEvent
     /**
      * Returns the response object.
      *
-     * @return Response
+     * @return Response|null
      */
     public function getResponse()
     {
diff --git a/src/Symfony/Component/Messenger/Transport/ChainSender.php b/src/Symfony/Component/Messenger/Transport/ChainSender.php
index 97e3ce44bb..2d2d55f03d 100644
--- a/src/Symfony/Component/Messenger/Transport/ChainSender.php
+++ b/src/Symfony/Component/Messenger/Transport/ChainSender.php
@@ -11,6 +11,8 @@
 
 namespace Symfony\Component\Messenger\Transport;
 
+use Symfony\Component\Messenger\Envelope;
+
 /**
  * @author Tobias Schultze <http://tobion.de>
  */
@@ -29,7 +31,7 @@ class ChainSender implements SenderInterface
     /**
      * {@inheritdoc}
      */
-    public function send($message): void
+    public function send(Envelope $message): void
     {
         foreach ($this->senders as $sender) {
             $sender->send($message);
diff --git a/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php
index f901712350..af0c45609c 100644
--- a/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php
@@ -294,7 +294,7 @@ abstract class AbstractObjectNormalizer extends AbstractNormalizer
      */
     private function validateAndDenormalize(string $currentClass, string $attribute, $data, ?string $format, array $context)
     {
-        if (null === $this->propertyTypeExtractor || null === $types = $this->propertyTypeExtractor->getTypes($currentClass, $attribute)) {
+        if (null === $types = $this->getTypes($currentClass, $attribute)) {
             return $data;
         }
 
@@ -357,6 +357,36 @@ abstract class AbstractObjectNormalizer extends AbstractNormalizer
         throw new NotNormalizableValueException(sprintf('The type of the "%s" attribute for class "%s" must be one of "%s" ("%s" given).', $attribute, $currentClass, implode('", "', array_keys($expectedTypes)), gettype($data)));
     }
 
+    /**
+     * @return Type[]|null
+     */
+    private function getTypes(string $currentClass, string $attribute)
+    {
+        if (null === $this->propertyTypeExtractor) {
+            return null;
+        }
+
+        if (null !== $types = $this->propertyTypeExtractor->getTypes($currentClass, $attribute)) {
+            return $types;
+        }
+
+        if (null !== $this->classDiscriminatorResolver && null !== $discriminatorMapping = $this->classDiscriminatorResolver->getMappingForClass($currentClass)) {
+            if ($discriminatorMapping->getTypeProperty() === $attribute) {
+                return array(
+                    new Type(Type::BUILTIN_TYPE_STRING),
+                );
+            }
+
+            foreach ($discriminatorMapping->getTypesMapping() as $mappedClass) {
+                if (null !== $types = $this->propertyTypeExtractor->getTypes($mappedClass, $attribute)) {
+                    return $types;
+                }
+            }
+        }
+
+        return null;
+    }
+
     /**
      * Sets an attribute and apply the name converter if necessary.
      *
diff --git a/src/Symfony/Component/Serializer/Tests/Fixtures/DummyMessageNumberTwo.php b/src/Symfony/Component/Serializer/Tests/Fixtures/DummyMessageNumberTwo.php
index 3b828e50bf..5a24e7c9ff 100644
--- a/src/Symfony/Component/Serializer/Tests/Fixtures/DummyMessageNumberTwo.php
+++ b/src/Symfony/Component/Serializer/Tests/Fixtures/DummyMessageNumberTwo.php
@@ -22,4 +22,19 @@ class DummyMessageNumberTwo implements DummyMessageInterface
      * @Groups({"two"})
      */
     public $three;
+
+    /**
+     * @var DummyMessageNumberOne
+     */
+    private $nested;
+
+    public function setNested(DummyMessageNumberOne $nested)
+    {
+        $this->nested = $nested;
+    }
+
+    public function getNested(): DummyMessageNumberOne
+    {
+        return $this->nested;
+    }
 }
diff --git a/src/Symfony/Component/Serializer/Tests/SerializerTest.php b/src/Symfony/Component/Serializer/Tests/SerializerTest.php
index 25fbbf38ce..743461a727 100644
--- a/src/Symfony/Component/Serializer/Tests/SerializerTest.php
+++ b/src/Symfony/Component/Serializer/Tests/SerializerTest.php
@@ -13,6 +13,7 @@ namespace Symfony\Component\Serializer\Tests;
 
 use Doctrine\Common\Annotations\AnnotationReader;
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\PropertyInfo\Extractor\ReflectionExtractor;
 use Symfony\Component\Serializer\Mapping\ClassDiscriminatorFromClassMetadata;
 use Symfony\Component\Serializer\Mapping\ClassDiscriminatorMapping;
 use Symfony\Component\Serializer\Mapping\ClassMetadata;
@@ -35,6 +36,7 @@ use Symfony\Component\Serializer\Tests\Fixtures\AbstractDummyFirstChild;
 use Symfony\Component\Serializer\Tests\Fixtures\AbstractDummySecondChild;
 use Symfony\Component\Serializer\Tests\Fixtures\DummyMessageInterface;
 use Symfony\Component\Serializer\Tests\Fixtures\DummyMessageNumberOne;
+use Symfony\Component\Serializer\Tests\Fixtures\DummyMessageNumberTwo;
 use Symfony\Component\Serializer\Tests\Fixtures\TraversableDummy;
 use Symfony\Component\Serializer\Tests\Fixtures\NormalizableTraversableDummy;
 use Symfony\Component\Serializer\Tests\Normalizer\TestNormalizer;
@@ -430,6 +432,22 @@ class SerializerTest extends TestCase
         $this->assertEquals('{"two":2,"type":"one"}', $serialized);
     }
 
+    public function testDeserializeAndSerializeNestedInterfacedObjectsWithTheClassMetadataDiscriminator()
+    {
+        $nested = new DummyMessageNumberOne();
+        $nested->one = 'foo';
+
+        $example = new DummyMessageNumberTwo();
+        $example->setNested($nested);
+
+        $serializer = $this->serializerWithClassDiscriminator();
+
+        $serialized = $serializer->serialize($example, 'json');
+        $deserialized = $serializer->deserialize($serialized, DummyMessageInterface::class, 'json');
+
+        $this->assertEquals($example, $deserialized);
+    }
+
     /**
      * @expectedException \Symfony\Component\Serializer\Exception\RuntimeException
      * @expectedExceptionMessage The type "second" has no mapped class for the abstract object "Symfony\Component\Serializer\Tests\Fixtures\DummyMessageInterface"
@@ -452,7 +470,7 @@ class SerializerTest extends TestCase
     {
         $classMetadataFactory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));
 
-        return new Serializer(array(new ObjectNormalizer($classMetadataFactory, null, null, null, new ClassDiscriminatorFromClassMetadata($classMetadataFactory))), array('json' => new JsonEncoder()));
+        return new Serializer(array(new ObjectNormalizer($classMetadataFactory, null, null, new ReflectionExtractor(), new ClassDiscriminatorFromClassMetadata($classMetadataFactory))), array('json' => new JsonEncoder()));
     }
 }
 
diff --git a/src/Symfony/Component/Translation/PluralizationRules.php b/src/Symfony/Component/Translation/PluralizationRules.php
index 48a6c608cb..94d9e4350c 100644
--- a/src/Symfony/Component/Translation/PluralizationRules.php
+++ b/src/Symfony/Component/Translation/PluralizationRules.php
@@ -144,6 +144,7 @@ class PluralizationRules
             case 'bs':
             case 'hr':
             case 'ru':
+            case 'sh':
             case 'sr':
             case 'uk':
                 return ((1 == $number % 10) && (11 != $number % 100)) ? 0 : ((($number % 10 >= 2) && ($number % 10 <= 4) && (($number % 100 < 10) || ($number % 100 >= 20))) ? 1 : 2);
diff --git a/src/Symfony/Component/Validator/Resources/translations/validators.ca.xlf b/src/Symfony/Component/Validator/Resources/translations/validators.ca.xlf
index 85b6970fc3..078a25d052 100644
--- a/src/Symfony/Component/Validator/Resources/translations/validators.ca.xlf
+++ b/src/Symfony/Component/Validator/Resources/translations/validators.ca.xlf
@@ -302,6 +302,10 @@
                 <source>An empty file is not allowed.</source>
                 <target>No està permès un fixter buit.</target>
             </trans-unit>
+            <trans-unit id="83">
+                <source>This is not a valid UUID.</source>
+                <target>Aquest valor no és un UUID vàlid.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/src/Symfony/Component/Validator/Resources/translations/validators.de.xlf b/src/Symfony/Component/Validator/Resources/translations/validators.de.xlf
index 6e89e17ec3..3e44e1e284 100644
--- a/src/Symfony/Component/Validator/Resources/translations/validators.de.xlf
+++ b/src/Symfony/Component/Validator/Resources/translations/validators.de.xlf
@@ -318,6 +318,10 @@
                 <source>Error</source>
                 <target>Fehler</target>
             </trans-unit>
+            <trans-unit id="83">
+                <source>This is not a valid UUID.</source>
+                <target>Dies ist keine gültige UUID.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/src/Symfony/Component/Validator/Resources/translations/validators.en.xlf b/src/Symfony/Component/Validator/Resources/translations/validators.en.xlf
index 7e0e9614de..3d173846a5 100644
--- a/src/Symfony/Component/Validator/Resources/translations/validators.en.xlf
+++ b/src/Symfony/Component/Validator/Resources/translations/validators.en.xlf
@@ -318,6 +318,10 @@
                 <source>Error</source>
                 <target>Error</target>
             </trans-unit>
+            <trans-unit id="83">
+                <source>This is not a valid UUID.</source>
+                <target>This is not a valid UUID.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/src/Symfony/Component/Validator/Resources/translations/validators.es.xlf b/src/Symfony/Component/Validator/Resources/translations/validators.es.xlf
index 948594d03e..25d5b8a5d3 100644
--- a/src/Symfony/Component/Validator/Resources/translations/validators.es.xlf
+++ b/src/Symfony/Component/Validator/Resources/translations/validators.es.xlf
@@ -318,6 +318,10 @@
                 <source>Error</source>
                 <target>Error</target>
             </trans-unit>
+            <trans-unit id="83">
+                <source>This is not a valid UUID.</source>
+                <target>Este valor no es un UUID válido.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/src/Symfony/Component/Validator/Resources/translations/validators.eu.xlf b/src/Symfony/Component/Validator/Resources/translations/validators.eu.xlf
index d4125fdb0f..d311dedb5e 100644
--- a/src/Symfony/Component/Validator/Resources/translations/validators.eu.xlf
+++ b/src/Symfony/Component/Validator/Resources/translations/validators.eu.xlf
@@ -282,6 +282,10 @@
                 <source>Error</source>
                 <target>Errore</target>
             </trans-unit>
+            <trans-unit id="83">
+                <source>This is not a valid UUID.</source>
+                <target>Balio hau ez da onartutako UUID bat.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/src/Symfony/Component/Validator/Resources/translations/validators.fr.xlf b/src/Symfony/Component/Validator/Resources/translations/validators.fr.xlf
index 6c1b4030f3..382acb975c 100644
--- a/src/Symfony/Component/Validator/Resources/translations/validators.fr.xlf
+++ b/src/Symfony/Component/Validator/Resources/translations/validators.fr.xlf
@@ -318,6 +318,10 @@
                 <source>Error</source>
                 <target>Erreur</target>
             </trans-unit>
+            <trans-unit id="83">
+                <source>This is not a valid UUID.</source>
+                <target>Ceci n'est pas un UUID valide.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/src/Symfony/Component/Validator/Resources/translations/validators.hu.xlf b/src/Symfony/Component/Validator/Resources/translations/validators.hu.xlf
index 3a8a1db6ee..1011d54818 100644
--- a/src/Symfony/Component/Validator/Resources/translations/validators.hu.xlf
+++ b/src/Symfony/Component/Validator/Resources/translations/validators.hu.xlf
@@ -318,6 +318,10 @@
                 <source>Error</source>
                 <target>Hiba</target>
             </trans-unit>
+            <trans-unit id="83">
+                <source>This is not a valid UUID.</source>
+                <target>Érvénytelen egyedi azonosító (UUID).</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/src/Symfony/Component/Validator/Resources/translations/validators.it.xlf b/src/Symfony/Component/Validator/Resources/translations/validators.it.xlf
index bd71ece6ae..f19544701d 100644
--- a/src/Symfony/Component/Validator/Resources/translations/validators.it.xlf
+++ b/src/Symfony/Component/Validator/Resources/translations/validators.it.xlf
@@ -318,6 +318,10 @@
                 <source>Error</source>
                 <target>Errore</target>
             </trans-unit>
+            <trans-unit id="83">
+                <source>This is not a valid UUID.</source>
+                <target>Questo non è un UUID valido.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>
diff --git a/src/Symfony/Component/Validator/Resources/translations/validators.nl.xlf b/src/Symfony/Component/Validator/Resources/translations/validators.nl.xlf
index 70ec678ec9..413a97eb17 100644
--- a/src/Symfony/Component/Validator/Resources/translations/validators.nl.xlf
+++ b/src/Symfony/Component/Validator/Resources/translations/validators.nl.xlf
@@ -314,6 +314,10 @@
                 <source>Error</source>
                 <target>Fout</target>
             </trans-unit>
+            <trans-unit id="83">
+                <source>This is not a valid UUID.</source>
+                <target>Deze waarde is geen geldige UUID waarde.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>