Merge branch '3.4' into 4.1

* 3.4:
  Remove duplicate condition
  fix useless space in docblock
  remove unneeded tearDown method
  [Intl] Update the ICU data to 63.1
  [FrameworkBundle] Fix broken exception message
  [TwigBundle] Fix usage of TwigBundle without FrameworkBundle
  Revert "fixed CS"
  Skip empty proxy code
  [Security] Fix "exclude-from-classmap"
  add missing double-quotes to extra_fields output message
  Convert InsufficientAuthenticationException to HttpException

Author: nicolas-grekas

Dumper/PhpDumper.php

@@ -373,7 +373,9 @@ private function generateProxyClasses()
             $alreadyGenerated[$class] = true;
             // register class' reflector for resource tracking
             $this->container->getReflectionClass($class);
-            $proxyCode = "\n".$proxyDumper->getProxyCode($definition);
+            if ("\n" === $proxyCode = "\n".$proxyDumper->getProxyCode($definition)) {
+                continue;
+            }
             if ($strip) {
                 $proxyCode = "<?php\n".$proxyCode;
                 $proxyCode = substr(Kernel::stripComments($proxyCode), 5);