diff --git a/src/Symfony/Component/Config/Definition/BaseNode.php b/src/Symfony/Component/Config/Definition/BaseNode.php
index 39511c15c6..866feb6e1a 100644
--- a/src/Symfony/Component/Config/Definition/BaseNode.php
+++ b/src/Symfony/Component/Config/Definition/BaseNode.php
@@ -47,7 +47,10 @@ abstract class BaseNode implements NodeInterface
      */
     public function __construct(?string $name, NodeInterface $parent = null, string $pathSeparator = self::DEFAULT_PATH_SEPARATOR)
     {
-        if (false !== strpos($name = (string) $name, $pathSeparator)) {
+        if (null === $name) {
+            $name = '';
+        }
+        if (false !== strpos($name, $pathSeparator)) {
             throw new \InvalidArgumentException('The name must not contain "'.$pathSeparator.'".');
         }
 
diff --git a/src/Symfony/Component/Config/Definition/Builder/NodeDefinition.php b/src/Symfony/Component/Config/Definition/Builder/NodeDefinition.php
index a771a43cd2..948a68f6b8 100644
--- a/src/Symfony/Component/Config/Definition/Builder/NodeDefinition.php
+++ b/src/Symfony/Component/Config/Definition/Builder/NodeDefinition.php
@@ -41,7 +41,7 @@ abstract class NodeDefinition implements NodeParentInterface
     public function __construct(?string $name, NodeParentInterface $parent = null)
     {
         $this->parent = $parent;
-        $this->name = $name;
+        $this->name = $name ?? '';
     }
 
     /**
diff --git a/src/Symfony/Component/Config/Resource/GlobResource.php b/src/Symfony/Component/Config/Resource/GlobResource.php
index fce8f6e206..e33cafc6e0 100644
--- a/src/Symfony/Component/Config/Resource/GlobResource.php
+++ b/src/Symfony/Component/Config/Resource/GlobResource.php
@@ -39,7 +39,7 @@ class GlobResource implements \IteratorAggregate, SelfCheckingResourceInterface
      *
      * @throws \InvalidArgumentException
      */
-    public function __construct(?string $prefix, string $pattern, bool $recursive, bool $forExclusion = false, array $excludedPrefixes = [])
+    public function __construct(string $prefix, string $pattern, bool $recursive, bool $forExclusion = false, array $excludedPrefixes = [])
     {
         $this->prefix = realpath($prefix) ?: (file_exists($prefix) ? $prefix : false);
         $this->pattern = $pattern;
diff --git a/src/Symfony/Component/Config/Tests/Loader/FileLoaderTest.php b/src/Symfony/Component/Config/Tests/Loader/FileLoaderTest.php
index b59ace46f9..0b2e3fb6b9 100644
--- a/src/Symfony/Component/Config/Tests/Loader/FileLoaderTest.php
+++ b/src/Symfony/Component/Config/Tests/Loader/FileLoaderTest.php
@@ -71,6 +71,7 @@ class FileLoaderTest extends TestCase
     public function testImportWithGlobLikeResource()
     {
         $locatorMock = $this->getMockBuilder('Symfony\Component\Config\FileLocatorInterface')->getMock();
+        $locatorMock->expects($this->once())->method('locate')->willReturn('');
         $loader = new TestFileLoader($locatorMock);
 
         $this->assertSame('[foo]', $loader->import('[foo]'));
@@ -79,6 +80,7 @@ class FileLoaderTest extends TestCase
     public function testImportWithNoGlobMatch()
     {
         $locatorMock = $this->getMockBuilder('Symfony\Component\Config\FileLocatorInterface')->getMock();
+        $locatorMock->expects($this->once())->method('locate')->willReturn('');
         $loader = new TestFileLoader($locatorMock);
 
         $this->assertNull($loader->import('./*.abc'));
diff --git a/src/Symfony/Component/DomCrawler/AbstractUriElement.php b/src/Symfony/Component/DomCrawler/AbstractUriElement.php
index 1ef51df59b..ead9dca25b 100644
--- a/src/Symfony/Component/DomCrawler/AbstractUriElement.php
+++ b/src/Symfony/Component/DomCrawler/AbstractUriElement.php
@@ -24,7 +24,7 @@ abstract class AbstractUriElement
     protected $node;
 
     /**
-     * @var string The method to use for the element
+     * @var string|null The method to use for the element
      */
     protected $method;
 
@@ -36,7 +36,7 @@ abstract class AbstractUriElement
     /**
      * @param \DOMElement $node       A \DOMElement instance
      * @param string      $currentUri The URI of the page where the link is embedded (or the base href)
-     * @param string      $method     The method to use for the link (GET by default)
+     * @param string|null $method     The method to use for the link (GET by default)
      *
      * @throws \InvalidArgumentException if the node is not a link
      */
@@ -70,7 +70,7 @@ abstract class AbstractUriElement
      */
     public function getMethod()
     {
-        return $this->method;
+        return $this->method ?? 'GET';
     }
 
     /**
diff --git a/src/Symfony/Component/Form/Extension/Validator/Constraints/FormValidator.php b/src/Symfony/Component/Form/Extension/Validator/Constraints/FormValidator.php
index ca3cf80fde..755eccbd1a 100644
--- a/src/Symfony/Component/Form/Extension/Validator/Constraints/FormValidator.php
+++ b/src/Symfony/Component/Form/Extension/Validator/Constraints/FormValidator.php
@@ -137,7 +137,7 @@ class FormValidator extends ConstraintValidator
         // Mark the form with an error if it contains extra fields
         if (!$config->getOption('allow_extra_fields') && \count($form->getExtraData()) > 0) {
             $this->context->setConstraint($formConstraint);
-            $this->context->buildViolation($config->getOption('extra_fields_message'))
+            $this->context->buildViolation($config->getOption('extra_fields_message', ''))
                 ->setParameter('{{ extra_fields }}', '"'.implode('", "', array_keys($form->getExtraData())).'"')
                 ->setInvalidValue($form->getExtraData())
                 ->setCode(Form::NO_SUCH_FIELD_ERROR)
diff --git a/src/Symfony/Component/Form/Form.php b/src/Symfony/Component/Form/Form.php
index aba3b0fae2..e041e40ff0 100644
--- a/src/Symfony/Component/Form/Form.php
+++ b/src/Symfony/Component/Form/Form.php
@@ -146,7 +146,7 @@ class Form implements \IteratorAggregate, FormInterface, ClearableErrorsInterfac
     private $lockSetData = false;
 
     /**
-     * @var string|int|null
+     * @var string|null
      */
     private $name;
 
@@ -847,6 +847,8 @@ class Form implements \IteratorAggregate, FormInterface, ClearableErrorsInterfac
                 throw new UnexpectedTypeException($child, 'string, integer or Symfony\Component\Form\FormInterface');
             }
 
+            $child = (string) $child;
+
             if (null !== $type && !\is_string($type) && !$type instanceof FormTypeInterface) {
                 throw new UnexpectedTypeException($type, 'string or Symfony\Component\Form\FormTypeInterface');
             }
diff --git a/src/Symfony/Component/Form/FormConfigBuilder.php b/src/Symfony/Component/Form/FormConfigBuilder.php
index fa7bac32bb..9effe1a7c6 100644
--- a/src/Symfony/Component/Form/FormConfigBuilder.php
+++ b/src/Symfony/Component/Form/FormConfigBuilder.php
@@ -107,7 +107,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     /**
      * Creates an empty form configuration.
      *
-     * @param string|int               $name       The form name
+     * @param string|null              $name       The form name
      * @param string|null              $dataClass  The class of the form's data
      * @param EventDispatcherInterface $dispatcher The event dispatcher
      * @param array                    $options    The form options
@@ -115,7 +115,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      * @throws InvalidArgumentException if the data class is not a valid class or if
      *                                  the name contains invalid characters
      */
-    public function __construct($name, ?string $dataClass, EventDispatcherInterface $dispatcher, array $options = [])
+    public function __construct(?string $name, ?string $dataClass, EventDispatcherInterface $dispatcher, array $options = [])
     {
         self::validateName($name);
 
@@ -123,7 +123,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
             throw new InvalidArgumentException(sprintf('Class "%s" not found. Is the "data_class" form option set correctly?', $dataClass));
         }
 
-        $this->name = (string) $name;
+        $this->name = $name ?? '';
         $this->dataClass = $dataClass;
         $this->dispatcher = $dispatcher;
         $this->options = $options;
@@ -767,15 +767,17 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     /**
      * Validates whether the given variable is a valid form name.
      *
-     * @param string|int|null $name The tested form name
+     * @param string|null $name The tested form name
      *
      * @throws UnexpectedTypeException  if the name is not a string or an integer
      * @throws InvalidArgumentException if the name contains invalid characters
+     *
+     * @internal since Symfony 4.4
      */
     public static function validateName($name)
     {
-        if (null !== $name && !\is_string($name) && !\is_int($name)) {
-            throw new UnexpectedTypeException($name, 'string, integer or null');
+        if (null !== $name && !\is_string($name)) {
+            throw new UnexpectedTypeException($name, 'string or null');
         }
 
         if (!self::isValidName($name)) {
@@ -792,12 +794,8 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      *   * starts with a letter, digit or underscore
      *   * contains only letters, digits, numbers, underscores ("_"),
      *     hyphens ("-") and colons (":")
-     *
-     * @param string|null $name The tested form name
-     *
-     * @return bool Whether the name is valid
      */
-    public static function isValidName($name)
+    final public static function isValidName(?string $name): bool
     {
         return '' === $name || null === $name || preg_match('/^[a-zA-Z0-9_][a-zA-Z0-9_\-:]*$/D', $name);
     }
diff --git a/src/Symfony/Component/Form/FormError.php b/src/Symfony/Component/Form/FormError.php
index f0898b7665..f390854aee 100644
--- a/src/Symfony/Component/Form/FormError.php
+++ b/src/Symfony/Component/Form/FormError.php
@@ -47,9 +47,9 @@ class FormError
      *
      * @see \Symfony\Component\Translation\Translator
      */
-    public function __construct(?string $message, string $messageTemplate = null, array $messageParameters = [], int $messagePluralization = null, $cause = null)
+    public function __construct(string $message, string $messageTemplate = null, array $messageParameters = [], int $messagePluralization = null, $cause = null)
     {
-        $this->message = (string) $message;
+        $this->message = $message;
         $this->messageTemplate = $messageTemplate ?: $message;
         $this->messageParameters = $messageParameters;
         $this->messagePluralization = $messagePluralization;
diff --git a/src/Symfony/Component/Form/FormFactory.php b/src/Symfony/Component/Form/FormFactory.php
index b397f9a21f..ac38b0a39e 100644
--- a/src/Symfony/Component/Form/FormFactory.php
+++ b/src/Symfony/Component/Form/FormFactory.php
@@ -73,7 +73,7 @@ class FormFactory implements FormFactoryInterface
 
         $type = $this->registry->getType($type);
 
-        $builder = $type->createBuilder($this, $name, $options);
+        $builder = $type->createBuilder($this, (string) $name, $options);
 
         // Explicitly call buildForm() in order to be able to override either
         // createBuilder() or buildForm() in the resolved form type
diff --git a/src/Symfony/Component/Form/Tests/Extension/Csrf/Type/FormTypeCsrfExtensionTest.php b/src/Symfony/Component/Form/Tests/Extension/Csrf/Type/FormTypeCsrfExtensionTest.php
index bde6c2808d..a46c3de6c7 100644
--- a/src/Symfony/Component/Form/Tests/Extension/Csrf/Type/FormTypeCsrfExtensionTest.php
+++ b/src/Symfony/Component/Form/Tests/Extension/Csrf/Type/FormTypeCsrfExtensionTest.php
@@ -46,6 +46,7 @@ class FormTypeCsrfExtensionTest extends TypeTestCase
     {
         $this->tokenManager = $this->getMockBuilder(CsrfTokenManagerInterface::class)->getMock();
         $this->translator = $this->getMockBuilder(TranslatorInterface::class)->getMock();
+        $this->translator->expects($this->any())->method('trans')->willReturnArgument(0);
 
         parent::setUp();
     }
@@ -371,16 +372,11 @@ class FormTypeCsrfExtensionTest extends TypeTestCase
             ->with($csrfToken)
             ->willReturn(false);
 
-        $this->translator->expects($this->once())
-             ->method('trans')
-             ->with('Foobar')
-             ->willReturn('[trans]Foobar[/trans]');
-
         $form = $this->factory
             ->createBuilder('Symfony\Component\Form\Extension\Core\Type\FormType', null, [
                 'csrf_field_name' => 'csrf',
                 'csrf_token_manager' => $this->tokenManager,
-                'csrf_message' => 'Foobar',
+                'csrf_message' => '[trans]Foobar[/trans]',
                 'csrf_token_id' => 'TOKEN_ID',
                 'compound' => true,
             ])
diff --git a/src/Symfony/Component/Form/Tests/FormConfigTest.php b/src/Symfony/Component/Form/Tests/FormConfigTest.php
index 18dac5528f..c241f09973 100644
--- a/src/Symfony/Component/Form/Tests/FormConfigTest.php
+++ b/src/Symfony/Component/Form/Tests/FormConfigTest.php
@@ -57,11 +57,6 @@ class FormConfigTest extends TestCase
             [123],
             // NULL is allowed
             [null],
-            // Other types are not
-            [1.23, 'Symfony\Component\Form\Exception\UnexpectedTypeException'],
-            [5., 'Symfony\Component\Form\Exception\UnexpectedTypeException'],
-            [true, 'Symfony\Component\Form\Exception\UnexpectedTypeException'],
-            [new \stdClass(), 'Symfony\Component\Form\Exception\UnexpectedTypeException'],
         ];
     }
 
diff --git a/src/Symfony/Component/HttpFoundation/RedirectResponse.php b/src/Symfony/Component/HttpFoundation/RedirectResponse.php
index 8d04aa42c9..c6b559beb1 100644
--- a/src/Symfony/Component/HttpFoundation/RedirectResponse.php
+++ b/src/Symfony/Component/HttpFoundation/RedirectResponse.php
@@ -32,7 +32,7 @@ class RedirectResponse extends Response
      *
      * @see http://tools.ietf.org/html/rfc2616#section-10.3
      */
-    public function __construct(?string $url, int $status = 302, array $headers = [])
+    public function __construct(string $url, int $status = 302, array $headers = [])
     {
         parent::__construct('', $status, $headers);
 
@@ -82,7 +82,7 @@ class RedirectResponse extends Response
      */
     public function setTargetUrl($url)
     {
-        if (empty($url)) {
+        if ('' == $url) {
             throw new \InvalidArgumentException('Cannot redirect to an empty URL.');
         }
 
diff --git a/src/Symfony/Component/HttpFoundation/Tests/RedirectResponseTest.php b/src/Symfony/Component/HttpFoundation/Tests/RedirectResponseTest.php
index 5f6a8ac088..24d703d52b 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/RedirectResponseTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/RedirectResponseTest.php
@@ -28,10 +28,11 @@ class RedirectResponseTest extends TestCase
 
     /**
      * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage Cannot redirect to an empty URL.
      */
-    public function testRedirectResponseConstructorNullUrl()
+    public function testRedirectResponseConstructorEmptyUrl()
     {
-        $response = new RedirectResponse(null);
+        $response = new RedirectResponse('');
     }
 
     /**
diff --git a/src/Symfony/Component/Validator/ConstraintViolation.php b/src/Symfony/Component/Validator/ConstraintViolation.php
index 8651913c3e..a0ce00e334 100644
--- a/src/Symfony/Component/Validator/ConstraintViolation.php
+++ b/src/Symfony/Component/Validator/ConstraintViolation.php
@@ -44,12 +44,12 @@ class ConstraintViolation implements ConstraintViolationInterface
      *                                         violation
      * @param int|null        $plural          The number for determining the plural
      *                                         form when translating the message
-     * @param mixed           $code            The error code of the violation
+     * @param string|null     $code            The error code of the violation
      * @param Constraint|null $constraint      The constraint whose validation
      *                                         caused the violation
      * @param mixed           $cause           The cause of the violation
      */
-    public function __construct(?string $message, ?string $messageTemplate, array $parameters, $root, ?string $propertyPath, $invalidValue, int $plural = null, $code = null, Constraint $constraint = null, $cause = null)
+    public function __construct(string $message, ?string $messageTemplate, array $parameters, $root, ?string $propertyPath, $invalidValue, int $plural = null, $code = null, Constraint $constraint = null, $cause = null)
     {
         $this->message = $message;
         $this->messageTemplate = $messageTemplate;
diff --git a/src/Symfony/Component/Validator/Test/ConstraintValidatorTestCase.php b/src/Symfony/Component/Validator/Test/ConstraintValidatorTestCase.php
index 35e78268d4..b4ec2037fc 100644
--- a/src/Symfony/Component/Validator/Test/ConstraintValidatorTestCase.php
+++ b/src/Symfony/Component/Validator/Test/ConstraintValidatorTestCase.php
@@ -99,6 +99,7 @@ abstract class ConstraintValidatorTestCase extends TestCase
     protected function createContext()
     {
         $translator = $this->getMockBuilder(TranslatorInterface::class)->getMock();
+        $translator->expects($this->any())->method('trans')->willReturnArgument(0);
         $validator = $this->getMockBuilder('Symfony\Component\Validator\Validator\ValidatorInterface')->getMock();
         $contextualValidator = $this->getMockBuilder('Symfony\Component\Validator\Validator\ContextualValidatorInterface')->getMock();
 
@@ -330,7 +331,7 @@ class ConstraintViolationAssertion
     private function getViolation()
     {
         return new ConstraintViolation(
-            null,
+            $this->message,
             $this->message,
             $this->parameters,
             $this->context->getRoot(),
diff --git a/src/Symfony/Component/Validator/Violation/ConstraintViolationBuilder.php b/src/Symfony/Component/Validator/Violation/ConstraintViolationBuilder.php
index c5b1d0b83f..553f17f14a 100644
--- a/src/Symfony/Component/Validator/Violation/ConstraintViolationBuilder.php
+++ b/src/Symfony/Component/Validator/Violation/ConstraintViolationBuilder.php
@@ -47,7 +47,7 @@ class ConstraintViolationBuilder implements ConstraintViolationBuilderInterface
     /**
      * @param TranslatorInterface $translator
      */
-    public function __construct(ConstraintViolationList $violations, Constraint $constraint, $message, array $parameters, $root, $propertyPath, $invalidValue, $translator, $translationDomain = null)
+    public function __construct(ConstraintViolationList $violations, Constraint $constraint, string $message, array $parameters, $root, string $propertyPath, $invalidValue, $translator, string $translationDomain = null)
     {
         if (!$translator instanceof LegacyTranslatorInterface && !$translator instanceof TranslatorInterface) {
             throw new \TypeError(sprintf('Argument 8 passed to %s() must be an instance of %s, %s given.', __METHOD__, TranslatorInterface::class, \is_object($translator) ? \get_class($translator) : \gettype($translator)));