diff --git a/src/Symfony/Bridge/PhpUnit/bin/simple-phpunit.php b/src/Symfony/Bridge/PhpUnit/bin/simple-phpunit.php
index 4dba981057..e9088bfe44 100644
--- a/src/Symfony/Bridge/PhpUnit/bin/simple-phpunit.php
+++ b/src/Symfony/Bridge/PhpUnit/bin/simple-phpunit.php
@@ -151,9 +151,9 @@ if ('disabled' === $getEnvVar('SYMFONY_DEPRECATIONS_HELPER')) {
 }
 
 $COMPOSER = file_exists($COMPOSER = $oldPwd.'/composer.phar')
-    || ($COMPOSER = rtrim('\\' === \DIRECTORY_SEPARATOR ? preg_replace('/[\r\n].*/', '', `where.exe composer.phar 2> NUL`) : `which composer.phar 2> /dev/null`))
-    || ($COMPOSER = rtrim('\\' === \DIRECTORY_SEPARATOR ? preg_replace('/[\r\n].*/', '', `where.exe composer 2> NUL`) : `which composer 2> /dev/null`))
-    || file_exists($COMPOSER = rtrim('\\' === \DIRECTORY_SEPARATOR ? `git rev-parse --show-toplevel 2> NUL` : `git rev-parse --show-toplevel 2> /dev/null`).\DIRECTORY_SEPARATOR.'composer.phar')
+    || ($COMPOSER = rtrim((string) ('\\' === \DIRECTORY_SEPARATOR ? preg_replace('/[\r\n].*/', '', `where.exe composer.phar 2> NUL`) : `which composer.phar 2> /dev/null`)))
+    || ($COMPOSER = rtrim((string) ('\\' === \DIRECTORY_SEPARATOR ? preg_replace('/[\r\n].*/', '', `where.exe composer 2> NUL`) : `which composer 2> /dev/null`)))
+    || file_exists($COMPOSER = rtrim((string) ('\\' === \DIRECTORY_SEPARATOR ? `git rev-parse --show-toplevel 2> NUL` : `git rev-parse --show-toplevel 2> /dev/null`)).\DIRECTORY_SEPARATOR.'composer.phar')
     ? ('#!/usr/bin/env php' === file_get_contents($COMPOSER, false, null, 0, 18) ? $PHP : '').' '.escapeshellarg($COMPOSER) // detect shell wrappers by looking at the shebang
     : 'composer';
 
diff --git a/src/Symfony/Component/BrowserKit/Cookie.php b/src/Symfony/Component/BrowserKit/Cookie.php
index 77b330c025..8b639af6e8 100644
--- a/src/Symfony/Component/BrowserKit/Cookie.php
+++ b/src/Symfony/Component/BrowserKit/Cookie.php
@@ -46,7 +46,7 @@ class Cookie
      * Sets a cookie.
      *
      * @param string      $name         The cookie name
-     * @param string      $value        The value of the cookie
+     * @param string|null $value        The value of the cookie
      * @param string|null $expires      The time the cookie expires
      * @param string|null $path         The path on the server in which the cookie will be available on
      * @param string      $domain       The domain that the cookie is available
@@ -62,7 +62,7 @@ class Cookie
             $this->rawValue = $value;
         } else {
             $this->value = $value;
-            $this->rawValue = rawurlencode($value);
+            $this->rawValue = rawurlencode($value ?? '');
         }
         $this->name = $name;
         $this->path = empty($path) ? '/' : $path;
diff --git a/src/Symfony/Component/CssSelector/XPath/Extension/NodeExtension.php b/src/Symfony/Component/CssSelector/XPath/Extension/NodeExtension.php
index 0e138229e4..aa6f3f7044 100644
--- a/src/Symfony/Component/CssSelector/XPath/Extension/NodeExtension.php
+++ b/src/Symfony/Component/CssSelector/XPath/Extension/NodeExtension.php
@@ -157,7 +157,7 @@ class NodeExtension extends AbstractExtension
     {
         $element = $node->getElement();
 
-        if ($this->hasFlag(self::ELEMENT_NAME_IN_LOWER_CASE)) {
+        if ($element && $this->hasFlag(self::ELEMENT_NAME_IN_LOWER_CASE)) {
             $element = strtolower($element);
         }
 
diff --git a/src/Symfony/Component/DependencyInjection/Compiler/CheckTypeDeclarationsPass.php b/src/Symfony/Component/DependencyInjection/Compiler/CheckTypeDeclarationsPass.php
index ac56fb1eb1..c6b17efd4a 100644
--- a/src/Symfony/Component/DependencyInjection/Compiler/CheckTypeDeclarationsPass.php
+++ b/src/Symfony/Component/DependencyInjection/Compiler/CheckTypeDeclarationsPass.php
@@ -205,7 +205,7 @@ final class CheckTypeDeclarationsPass extends AbstractRecursivePass
         if ($value instanceof Definition) {
             $class = $value->getClass();
 
-            if (isset(self::BUILTIN_TYPES[strtolower($class)])) {
+            if ($class && isset(self::BUILTIN_TYPES[strtolower($class)])) {
                 $class = strtolower($class);
             } elseif (!$class || (!$this->autoload && !class_exists($class, false) && !interface_exists($class, false))) {
                 return;
diff --git a/src/Symfony/Component/DependencyInjection/Compiler/RegisterServiceSubscribersPass.php b/src/Symfony/Component/DependencyInjection/Compiler/RegisterServiceSubscribersPass.php
index 14bf000863..7373c95ab7 100644
--- a/src/Symfony/Component/DependencyInjection/Compiler/RegisterServiceSubscribersPass.php
+++ b/src/Symfony/Component/DependencyInjection/Compiler/RegisterServiceSubscribersPass.php
@@ -88,10 +88,12 @@ class RegisterServiceSubscribersPass extends AbstractRecursivePass
                 $serviceMap[$key] = new Reference($type);
             }
 
-            if (false !== $i = strpos($name, '::get')) {
-                $name = lcfirst(substr($name, 5 + $i));
-            } elseif (false !== strpos($name, '::')) {
-                $name = null;
+            if ($name) {
+                if (false !== $i = strpos($name, '::get')) {
+                    $name = lcfirst(substr($name, 5 + $i));
+                } elseif (false !== strpos($name, '::')) {
+                    $name = null;
+                }
             }
 
             if (null !== $name && !$this->container->has($name) && !$this->container->has($type.' $'.$name)) {
diff --git a/src/Symfony/Component/DependencyInjection/Compiler/ResolveBindingsPass.php b/src/Symfony/Component/DependencyInjection/Compiler/ResolveBindingsPass.php
index d99730d776..70dd04601c 100644
--- a/src/Symfony/Component/DependencyInjection/Compiler/ResolveBindingsPass.php
+++ b/src/Symfony/Component/DependencyInjection/Compiler/ResolveBindingsPass.php
@@ -178,7 +178,7 @@ class ResolveBindingsPass extends AbstractRecursivePass
 
                 $typeHint = ProxyHelper::getTypeHint($reflectionMethod, $parameter);
 
-                if (\array_key_exists($k = ltrim($typeHint, '\\').' $'.$parameter->name, $bindings)) {
+                if ($typeHint && \array_key_exists($k = ltrim($typeHint, '\\').' $'.$parameter->name, $bindings)) {
                     $arguments[$key] = $this->getBindingValue($bindings[$k]);
 
                     continue;
diff --git a/src/Symfony/Component/DomCrawler/AbstractUriElement.php b/src/Symfony/Component/DomCrawler/AbstractUriElement.php
index ea13438be3..83b2433c8f 100644
--- a/src/Symfony/Component/DomCrawler/AbstractUriElement.php
+++ b/src/Symfony/Component/DomCrawler/AbstractUriElement.php
@@ -47,7 +47,7 @@ abstract class AbstractUriElement
         $this->currentUri = $currentUri;
 
         $elementUriIsRelative = null === parse_url(trim($this->getRawUri()), \PHP_URL_SCHEME);
-        $baseUriIsAbsolute = \in_array(strtolower(substr($this->currentUri, 0, 4)), ['http', 'file']);
+        $baseUriIsAbsolute = null !== $this->currentUri && \in_array(strtolower(substr($this->currentUri, 0, 4)), ['http', 'file']);
         if ($elementUriIsRelative && !$baseUriIsAbsolute) {
             throw new \InvalidArgumentException(sprintf('The URL of the element is relative, so you must define its base URI passing an absolute URL to the constructor of the "%s" class ("%s" was passed).', __CLASS__, $this->currentUri));
         }
diff --git a/src/Symfony/Component/Finder/Comparator/NumberComparator.php b/src/Symfony/Component/Finder/Comparator/NumberComparator.php
index 78e1bd3b34..657118fb6b 100644
--- a/src/Symfony/Component/Finder/Comparator/NumberComparator.php
+++ b/src/Symfony/Component/Finder/Comparator/NumberComparator.php
@@ -41,8 +41,8 @@ class NumberComparator extends Comparator
      */
     public function __construct(?string $test)
     {
-        if (!preg_match('#^\s*(==|!=|[<>]=?)?\s*([0-9\.]+)\s*([kmg]i?)?\s*$#i', $test, $matches)) {
-            throw new \InvalidArgumentException(sprintf('Don\'t understand "%s" as a number test.', $test));
+        if (null === $test || !preg_match('#^\s*(==|!=|[<>]=?)?\s*([0-9\.]+)\s*([kmg]i?)?\s*$#i', $test, $matches)) {
+            throw new \InvalidArgumentException(sprintf('Don\'t understand "%s" as a number test.', $test ?? 'null'));
         }
 
         $target = $matches[2];
diff --git a/src/Symfony/Component/HttpKernel/DependencyInjection/RegisterControllerArgumentLocatorsPass.php b/src/Symfony/Component/HttpKernel/DependencyInjection/RegisterControllerArgumentLocatorsPass.php
index 40c850cf66..cf4ab60284 100644
--- a/src/Symfony/Component/HttpKernel/DependencyInjection/RegisterControllerArgumentLocatorsPass.php
+++ b/src/Symfony/Component/HttpKernel/DependencyInjection/RegisterControllerArgumentLocatorsPass.php
@@ -124,7 +124,7 @@ class RegisterControllerArgumentLocatorsPass implements CompilerPassInterface
                 $args = [];
                 foreach ($parameters as $p) {
                     /** @var \ReflectionParameter $p */
-                    $type = ltrim($target = ProxyHelper::getTypeHint($r, $p), '\\');
+                    $type = ltrim($target = (string) ProxyHelper::getTypeHint($r, $p), '\\');
                     $invalidBehavior = ContainerInterface::IGNORE_ON_INVALID_REFERENCE;
 
                     if (isset($arguments[$r->name][$p->name])) {
diff --git a/src/Symfony/Component/HttpKernel/EventListener/RouterListener.php b/src/Symfony/Component/HttpKernel/EventListener/RouterListener.php
index 0071979688..47ee87b103 100644
--- a/src/Symfony/Component/HttpKernel/EventListener/RouterListener.php
+++ b/src/Symfony/Component/HttpKernel/EventListener/RouterListener.php
@@ -164,7 +164,7 @@ class RouterListener implements EventSubscriberInterface
     private function createWelcomeResponse(): Response
     {
         $version = Kernel::VERSION;
-        $projectDir = realpath($this->projectDir).\DIRECTORY_SEPARATOR;
+        $projectDir = realpath((string) $this->projectDir).\DIRECTORY_SEPARATOR;
         $docVersion = substr(Kernel::VERSION, 0, 3);
 
         ob_start();
diff --git a/src/Symfony/Component/HttpKernel/Tests/HttpCache/HttpCacheTest.php b/src/Symfony/Component/HttpKernel/Tests/HttpCache/HttpCacheTest.php
index d9dd572bf1..9bec2f7c94 100644
--- a/src/Symfony/Component/HttpKernel/Tests/HttpCache/HttpCacheTest.php
+++ b/src/Symfony/Component/HttpKernel/Tests/HttpCache/HttpCacheTest.php
@@ -212,8 +212,8 @@ class HttpCacheTest extends HttpCacheTestCase
 
     public function testValidatesPrivateResponsesCachedOnTheClient()
     {
-        $this->setNextResponse(200, [], '', function ($request, $response) {
-            $etags = preg_split('/\s*,\s*/', $request->headers->get('IF_NONE_MATCH'));
+        $this->setNextResponse(200, [], '', function (Request $request, $response) {
+            $etags = preg_split('/\s*,\s*/', $request->headers->get('IF_NONE_MATCH', ''));
             if ($request->cookies->has('authenticated')) {
                 $response->headers->set('Cache-Control', 'private, no-store');
                 $response->setETag('"private tag"');
diff --git a/src/Symfony/Component/Ldap/Tests/Adapter/ExtLdap/AdapterTest.php b/src/Symfony/Component/Ldap/Tests/Adapter/ExtLdap/AdapterTest.php
index d7b06c6b35..566ba215dc 100644
--- a/src/Symfony/Component/Ldap/Tests/Adapter/ExtLdap/AdapterTest.php
+++ b/src/Symfony/Component/Ldap/Tests/Adapter/ExtLdap/AdapterTest.php
@@ -30,7 +30,7 @@ class AdapterTest extends LdapTestCase
     {
         $ldap = new Adapter();
 
-        $this->assertEquals('\20foo\3dbar\0d(baz)*\20', $ldap->escape(" foo=bar\r(baz)* ", null, LdapInterface::ESCAPE_DN));
+        $this->assertEquals('\20foo\3dbar\0d(baz)*\20', $ldap->escape(" foo=bar\r(baz)* ", '', LdapInterface::ESCAPE_DN));
     }
 
     /**
diff --git a/src/Symfony/Component/Mime/Email.php b/src/Symfony/Component/Mime/Email.php
index 940cf489c0..7a7a0db32e 100644
--- a/src/Symfony/Component/Mime/Email.php
+++ b/src/Symfony/Component/Mime/Email.php
@@ -266,7 +266,7 @@ class Email extends Message
      */
     public function getPriority(): int
     {
-        [$priority] = sscanf($this->getHeaders()->getHeaderBody('X-Priority'), '%[1-5]');
+        [$priority] = sscanf($this->getHeaders()->getHeaderBody('X-Priority') ?? '', '%[1-5]');
 
         return $priority ?? 3;
     }
diff --git a/src/Symfony/Component/Routing/Generator/UrlGenerator.php b/src/Symfony/Component/Routing/Generator/UrlGenerator.php
index 7adf2ed27e..58d4384883 100644
--- a/src/Symfony/Component/Routing/Generator/UrlGenerator.php
+++ b/src/Symfony/Component/Routing/Generator/UrlGenerator.php
@@ -188,7 +188,7 @@ class UrlGenerator implements UrlGeneratorInterface, ConfigurableRequirementsInt
 
                 if (!$optional || $important || !\array_key_exists($varName, $defaults) || (null !== $mergedParams[$varName] && (string) $mergedParams[$varName] !== (string) $defaults[$varName])) {
                     // check requirement (while ignoring look-around patterns)
-                    if (null !== $this->strictRequirements && !preg_match('#^'.preg_replace('/\(\?(?:=|<=|!|<!)((?:[^()\\\\]+|\\\\.|\((?1)\))*)\)/', '', $token[2]).'$#i'.(empty($token[4]) ? '' : 'u'), $mergedParams[$token[3]])) {
+                    if (null !== $this->strictRequirements && !preg_match('#^'.preg_replace('/\(\?(?:=|<=|!|<!)((?:[^()\\\\]+|\\\\.|\((?1)\))*)\)/', '', $token[2]).'$#i'.(empty($token[4]) ? '' : 'u'), $mergedParams[$token[3]] ?? '')) {
                         if ($this->strictRequirements) {
                             throw new InvalidParameterException(strtr($message, ['{parameter}' => $varName, '{route}' => $name, '{expected}' => $token[2], '{given}' => $mergedParams[$varName]]));
                         }
diff --git a/src/Symfony/Component/Security/Core/Tests/Authentication/Provider/LdapBindAuthenticationProviderTest.php b/src/Symfony/Component/Security/Core/Tests/Authentication/Provider/LdapBindAuthenticationProviderTest.php
index 0605df44e0..2bc2d0176a 100644
--- a/src/Symfony/Component/Security/Core/Tests/Authentication/Provider/LdapBindAuthenticationProviderTest.php
+++ b/src/Symfony/Component/Security/Core/Tests/Authentication/Provider/LdapBindAuthenticationProviderTest.php
@@ -70,6 +70,7 @@ class LdapBindAuthenticationProviderTest extends TestCase
             ->method('bind')
             ->willThrowException(new ConnectionException())
         ;
+        $ldap->method('escape')->willReturnArgument(0);
         $userChecker = $this->createMock(UserCheckerInterface::class);
 
         $provider = new LdapBindAuthenticationProvider($userProvider, $userChecker, 'key', $ldap);
@@ -207,6 +208,7 @@ class LdapBindAuthenticationProviderTest extends TestCase
             ->method('query')
             ->willReturn($query)
         ;
+        $ldap->method('escape')->willReturnArgument(0);
         $userChecker = $this->createMock(UserCheckerInterface::class);
 
         $provider = new LdapBindAuthenticationProvider($userProvider, $userChecker, 'key', $ldap, '{username}', true, 'elsa', 'test1234A$');
diff --git a/src/Symfony/Component/Security/Http/Firewall/UsernamePasswordJsonAuthenticationListener.php b/src/Symfony/Component/Security/Http/Firewall/UsernamePasswordJsonAuthenticationListener.php
index d2d77f0a13..c75caf3427 100644
--- a/src/Symfony/Component/Security/Http/Firewall/UsernamePasswordJsonAuthenticationListener.php
+++ b/src/Symfony/Component/Security/Http/Firewall/UsernamePasswordJsonAuthenticationListener.php
@@ -82,8 +82,8 @@ class UsernamePasswordJsonAuthenticationListener extends AbstractListener implem
 
     public function supports(Request $request): ?bool
     {
-        if (false === strpos($request->getRequestFormat(), 'json')
-            && false === strpos($request->getContentType(), 'json')
+        if (false === strpos($request->getRequestFormat() ?? '', 'json')
+            && false === strpos($request->getContentType() ?? '', 'json')
         ) {
             return false;
         }
diff --git a/src/Symfony/Component/Translation/Loader/XliffFileLoader.php b/src/Symfony/Component/Translation/Loader/XliffFileLoader.php
index 11a721f455..a949e59ce4 100644
--- a/src/Symfony/Component/Translation/Loader/XliffFileLoader.php
+++ b/src/Symfony/Component/Translation/Loader/XliffFileLoader.php
@@ -129,7 +129,7 @@ class XliffFileLoader implements LoaderInterface
     private function extractXliff2(\DOMDocument $dom, MessageCatalogue $catalogue, string $domain)
     {
         $xml = simplexml_import_dom($dom);
-        $encoding = strtoupper($dom->encoding);
+        $encoding = $dom->encoding ? strtoupper($dom->encoding) : null;
 
         $xml->registerXPathNamespace('xliff', 'urn:oasis:names:tc:xliff:document:2.0');
 
diff --git a/src/Symfony/Component/Translation/Translator.php b/src/Symfony/Component/Translation/Translator.php
index f3d8d620ed..0f03b5afc3 100644
--- a/src/Symfony/Component/Translation/Translator.php
+++ b/src/Symfony/Component/Translation/Translator.php
@@ -507,7 +507,7 @@ EOF
      */
     protected function assertValidLocale($locale)
     {
-        if (1 !== preg_match('/^[a-z0-9@_\\.\\-]*$/i', $locale)) {
+        if (null !== $locale && 1 !== preg_match('/^[a-z0-9@_\\.\\-]*$/i', $locale)) {
             throw new InvalidArgumentException(sprintf('Invalid "%s" locale.', $locale));
         }
     }
diff --git a/src/Symfony/Component/Validator/Constraints/IpValidator.php b/src/Symfony/Component/Validator/Constraints/IpValidator.php
index 11d3f52cd3..e48d41e6d4 100644
--- a/src/Symfony/Component/Validator/Constraints/IpValidator.php
+++ b/src/Symfony/Component/Validator/Constraints/IpValidator.php
@@ -93,7 +93,7 @@ class IpValidator extends ConstraintValidator
                break;
 
             default:
-                $flag = null;
+                $flag = 0;
                 break;
         }
 
diff --git a/src/Symfony/Component/Yaml/Parser.php b/src/Symfony/Component/Yaml/Parser.php
index e2e82ddb22..32e6d34fe1 100644
--- a/src/Symfony/Component/Yaml/Parser.php
+++ b/src/Symfony/Component/Yaml/Parser.php
@@ -616,7 +616,7 @@ class Parser
         $data = [];
 
         if ($this->getCurrentLineIndentation() >= $newIndent) {
-            $data[] = substr($this->currentLine, $newIndent);
+            $data[] = substr($this->currentLine, $newIndent ?? 0);
         } elseif ($this->isCurrentLineEmpty() || $this->isCurrentLineComment()) {
             $data[] = $this->currentLine;
         } else {