Merge branch '4.4' into 5.4

* 4.4:
  [HttpClient] Fix the CS fix
  Workaround disabled "var_dump"
  [Serializer] Respect default context in DateTimeNormalizer::denormalize

# Conflicts:
#	src/Symfony/Component/Debug/ErrorHandler.php
#	src/Symfony/Component/HttpClient/HttpClientTrait.php
#	src/Symfony/Component/HttpKernel/EventListener/DebugHandlersListener.php

Author: ogizanagi

HttpClientTrait.php

@@ -117,7 +117,7 @@ private static function prepareRequest(?string $method, ?string $url, array $opt
         }
 
         // Validate on_progress
-        if (!\is_callable($onProgress = $options['on_progress'] ?? 'var_dump')) {
+        if (isset($options['on_progress']) && !\is_callable($onProgress = $options['on_progress'])) {
             throw new InvalidArgumentException(sprintf('Option "on_progress" must be callable, "%s" given.', get_debug_type($onProgress)));
         }
 
@@ -206,9 +206,11 @@ private static function mergeDefaultOptions(array $options, array $defaultOption
 
         $options += $defaultOptions;
 
-        foreach (self::$emptyDefaults ?? [] as $k => $v) {
-            if (!isset($options[$k])) {
-                $options[$k] = $v;
+        if (isset(self::$emptyDefaults)) {
+            foreach (self::$emptyDefaults as $k => $v) {
+                if (!isset($options[$k])) {
+                    $options[$k] = $v;
+                }
             }
         }