Fix tests on 5.6

src/Symfony/Component/Console/Input/ArgvInput.php

@@ -49,7 +49,7 @@ class ArgvInput extends Input
      */
     public function __construct(array $argv = null, InputDefinition $definition = null)
     {
-        $argv = $argv ?? $_SERVER['argv'] ?? [];
+        $argv = null !== $argv ? $argv : (isset($_SERVER['argv']) ? $_SERVER['argv'] : []);
 
         // strip the application name
         array_shift($argv);