Merge branch '3.4' into 4.1

* 3.4:
  [Routing] fix trailing slash redirection when using RedirectableUrlMatcher
  [PropertyAccessor] fix encoding of cache keys
  [WebProfiler] Detect empty file paths in file viewer
  fixed CS
  Changes for upcoming Travis' infra migration
  Doc fix: clarify isMethodCacheable() returns true only for GET & HEAD
  [DomCrawler] exclude fields inside "template" tags
  Use XLIFF source rather than resname when there's no target
  [DoctrineBridge] catch errors while converting to db values in data collector
  [DoctrineBridge] fix case sensitivity issue in RememberMe\DoctrineTokenProvider
  [EventDispatcher] Unwrap wrapped listeners internally
  Indentation error
  [HttpFoundation] Fix trailing space for mime-type with parameters
  [HttpFoundation] Fixed absolute Request URI with default port
  properly parse backslashes in unquoted env vars
  Use intersection type when referring to ParentNodeDefinitionInterface
  [BrowserKit] fixed BC Break for HTTP_HOST header; implemented same behaviour for HTTPS server parameter

Author: nicolas-grekas

Extension/CodeExtension.php

@@ -134,7 +134,7 @@ public function formatArgsAsText($args)
      */
     public function fileExcerpt($file, $line, $srcContext = 3)
     {
-        if (is_readable($file)) {
+        if (is_file($file) && is_readable($file)) {
             // highlight_file could throw warnings
             // see https://bugs.php.net/bug.php?id=25725
             $code = @highlight_file($file, true);
@@ -157,6 +157,8 @@ public function fileExcerpt($file, $line, $srcContext = 3)
 
             return '<ol start="'.max($line - $srcContext, 1).'">'.implode("\n", $lines).'</ol>';
         }
+
+        return null;
     }
 
     /**