Merge branch '3.4' into 4.0

* 3.4:
  [HttpKernel] Better handling of legacy cache
  modify definitions only if the do exist
  [DI] Prevent a ReflectionException during cache:clear when the parent class doesn't exist
  [FrameworkBundle] Make MicroKernelTraitTest green
  don't override existing verbosity env var
  [HttpKernel] Read $_ENV when checking SHELL_VERBOSITY
  Remove unreachable code
  Automatically enable the CSRF protection if CSRF manager exists
  bumped Symfony version to 3.4.0
  adding checks for the expression language
  updated VERSION for 3.4.0-RC2
  updated CHANGELOG for 3.4.0-RC2

Author: xabbuh

DependencyInjection/TranslatorPass.php

@@ -64,8 +64,15 @@ public function process(ContainerBuilder $container)
             ->replaceArgument(3, $loaders)
         ;
 
-        if ($container->hasParameter('twig.default_path')) {
+        if (!$container->hasParameter('twig.default_path')) {
+            return;
+        }
+
+        if ($container->hasDefinition($this->debugCommandServiceId)) {
             $container->getDefinition($this->debugCommandServiceId)->replaceArgument(4, $container->getParameter('twig.default_path'));
+        }
+
+        if ($container->hasDefinition($this->updateCommandServiceId)) {
             $container->getDefinition($this->updateCommandServiceId)->replaceArgument(5, $container->getParameter('twig.default_path'));
         }
     }