diff --git a/src/Symfony/Component/Cache/Traits/RedisTrait.php b/src/Symfony/Component/Cache/Traits/RedisTrait.php
index b247b115fa..5a9592a901 100644
--- a/src/Symfony/Component/Cache/Traits/RedisTrait.php
+++ b/src/Symfony/Component/Cache/Traits/RedisTrait.php
@@ -41,7 +41,7 @@ trait RedisTrait
     /**
      * @param \Redis|\RedisArray|\RedisCluster|\Predis\Client $redisClient
      */
-    public function init($redisClient, $namespace = '', $defaultLifetime = 0)
+    private function init($redisClient, $namespace = '', $defaultLifetime = 0)
     {
         parent::__construct($namespace, $defaultLifetime);
 
diff --git a/src/Symfony/Component/DependencyInjection/Loader/Configurator/DefaultsConfigurator.php b/src/Symfony/Component/DependencyInjection/Loader/Configurator/DefaultsConfigurator.php
index aec0b2bd21..07f6b7257e 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/Configurator/DefaultsConfigurator.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/Configurator/DefaultsConfigurator.php
@@ -34,12 +34,12 @@ class DefaultsConfigurator extends AbstractServiceConfigurator
      */
     final public function tag(string $name, array $attributes = array())
     {
-        if (!is_string($name) || '' === $name) {
+        if ('' === $name) {
             throw new InvalidArgumentException('The tag name in "_defaults" must be a non-empty string.');
         }
 
         foreach ($attributes as $attribute => $value) {
-            if (!is_scalar($value) && null !== $value) {
+            if (null !== $value && !is_scalar($value)) {
                 throw new InvalidArgumentException(sprintf('Tag "%s", attribute "%s" in "_defaults" must be of a scalar-type.', $name, $attribute));
             }
         }
diff --git a/src/Symfony/Component/Form/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformer.php b/src/Symfony/Component/Form/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformer.php
index 760e8aa664..301ead682b 100644
--- a/src/Symfony/Component/Form/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformer.php
+++ b/src/Symfony/Component/Form/Extension/Core/DataTransformer/IntegerToLocalizedStringTransformer.php
@@ -28,10 +28,6 @@ class IntegerToLocalizedStringTransformer extends NumberToLocalizedStringTransfo
      */
     public function __construct(?int $scale = 0, ?bool $grouping = false, int $roundingMode = self::ROUND_DOWN)
     {
-        if (null === $roundingMode) {
-            $roundingMode = self::ROUND_DOWN;
-        }
-
         parent::__construct(0, $grouping, $roundingMode);
     }
 
diff --git a/src/Symfony/Component/Security/Core/Authentication/RememberMe/PersistentToken.php b/src/Symfony/Component/Security/Core/Authentication/RememberMe/PersistentToken.php
index 996ad285fd..7c12706e3c 100644
--- a/src/Symfony/Component/Security/Core/Authentication/RememberMe/PersistentToken.php
+++ b/src/Symfony/Component/Security/Core/Authentication/RememberMe/PersistentToken.php
@@ -29,7 +29,7 @@ final class PersistentToken implements PersistentTokenInterface
         if (empty($class)) {
             throw new \InvalidArgumentException('$class must not be empty.');
         }
-        if ('' === $username || null === $username) {
+        if ('' === $username) {
             throw new \InvalidArgumentException('$username must not be empty.');
         }
         if (empty($series)) {
diff --git a/src/Symfony/Component/Security/Core/User/LdapUserProvider.php b/src/Symfony/Component/Security/Core/User/LdapUserProvider.php
index fcc3bcdb42..b3fa3fa6b9 100644
--- a/src/Symfony/Component/Security/Core/User/LdapUserProvider.php
+++ b/src/Symfony/Component/Security/Core/User/LdapUserProvider.php
@@ -37,10 +37,6 @@ class LdapUserProvider implements UserProviderInterface
 
     public function __construct(LdapInterface $ldap, string $baseDn, string $searchDn = null, string $searchPassword = null, array $defaultRoles = array(), string $uidKey = 'sAMAccountName', string $filter = '({uid_key}={username})', string $passwordAttribute = null)
     {
-        if (null === $uidKey) {
-            $uidKey = 'sAMAccountName';
-        }
-
         $this->ldap = $ldap;
         $this->baseDn = $baseDn;
         $this->searchDn = $searchDn;
diff --git a/src/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php
index 121e01530d..08d6ff79db 100644
--- a/src/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php
@@ -212,11 +212,17 @@ abstract class AbstractNormalizer implements NormalizerInterface, DenormalizerIn
      * @param array         $context
      * @param bool          $attributesAsString If false, return an array of {@link AttributeMetadataInterface}
      *
+     * @throws LogicException if the 'allow_extra_attributes' context variable is false and no class metadata factory is provided
+     *
      * @return string[]|AttributeMetadataInterface[]|bool
      */
     protected function getAllowedAttributes($classOrObject, array $context, $attributesAsString = false)
     {
         if (!$this->classMetadataFactory) {
+            if (isset($context[static::ALLOW_EXTRA_ATTRIBUTES]) && !$context[static::ALLOW_EXTRA_ATTRIBUTES]) {
+                throw new LogicException(sprintf('A class metadata factory must be provided in the constructor when setting "%s" to false.', static::ALLOW_EXTRA_ATTRIBUTES));
+            }
+
             return false;
         }
 
diff --git a/src/Symfony/Component/Serializer/Normalizer/NormalizerInterface.php b/src/Symfony/Component/Serializer/Normalizer/NormalizerInterface.php
index 5d0e3d1495..5cccdb3360 100644
--- a/src/Symfony/Component/Serializer/Normalizer/NormalizerInterface.php
+++ b/src/Symfony/Component/Serializer/Normalizer/NormalizerInterface.php
@@ -25,7 +25,7 @@ interface NormalizerInterface
     /**
      * Normalizes an object into a set of arrays/scalars.
      *
-     * @param object $object  Object to normalize
+     * @param mixed  $object  Object to normalize
      * @param string $format  Format the normalization result will be encoded as
      * @param array  $context Context options for the normalizer
      *
diff --git a/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php b/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php
index 21943e3600..7aa6a76a7d 100644
--- a/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php
+++ b/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php
@@ -19,6 +19,7 @@ use Symfony\Component\Serializer\Exception\NotNormalizableValueException;
 use Symfony\Component\Serializer\Mapping\Factory\ClassMetadataFactory;
 use Symfony\Component\Serializer\Mapping\Loader\AnnotationLoader;
 use Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer;
+use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
 use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;
 use Symfony\Component\Serializer\SerializerAwareInterface;
 use Symfony\Component\Serializer\SerializerInterface;
@@ -52,7 +53,8 @@ class AbstractObjectNormalizerTest extends TestCase
      */
     public function testDenormalizeWithExtraAttributes()
     {
-        $normalizer = new AbstractObjectNormalizerDummy();
+        $factory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));
+        $normalizer = new AbstractObjectNormalizerDummy($factory);
         $normalizer->denormalize(
             array('fooFoo' => 'foo', 'fooBar' => 'bar'),
             __NAMESPACE__.'\Dummy',
@@ -144,6 +146,21 @@ class AbstractObjectNormalizerTest extends TestCase
 
         return $denormalizer;
     }
+
+    /**
+     * Test that additional attributes throw an exception if no metadata factory is specified.
+     *
+     * @expectedException \Symfony\Component\Serializer\Exception\LogicException
+     * @expectedExceptionMessage A class metadata factory must be provided in the constructor when setting "allow_extra_attributes" to false.
+     */
+    public function testExtraAttributesException()
+    {
+        $normalizer = new ObjectNormalizer();
+
+        $normalizer->denormalize(array(), \stdClass::class, 'xml', array(
+            'allow_extra_attributes' => false,
+        ));
+    }
 }
 
 class AbstractObjectNormalizerDummy extends AbstractObjectNormalizer
diff --git a/src/Symfony/Component/Translation/Extractor/AbstractFileExtractor.php b/src/Symfony/Component/Translation/Extractor/AbstractFileExtractor.php
index 40b36451da..bdfec1a9ed 100644
--- a/src/Symfony/Component/Translation/Extractor/AbstractFileExtractor.php
+++ b/src/Symfony/Component/Translation/Extractor/AbstractFileExtractor.php
@@ -45,7 +45,7 @@ abstract class AbstractFileExtractor
 
     private function toSplFileInfo(string $file): \SplFileInfo
     {
-        return ($file instanceof \SplFileInfo) ? $file : new \SplFileInfo($file);
+        return new \SplFileInfo($file);
     }
 
     /**