diff --git a/src/Symfony/Component/VarDumper/Dumper/ContextProvider/CliContextProvider.php b/src/Symfony/Component/VarDumper/Dumper/ContextProvider/CliContextProvider.php
index e7f8ccf17f..38f878971c 100644
--- a/src/Symfony/Component/VarDumper/Dumper/ContextProvider/CliContextProvider.php
+++ b/src/Symfony/Component/VarDumper/Dumper/ContextProvider/CliContextProvider.php
@@ -25,7 +25,7 @@ final class CliContextProvider implements ContextProviderInterface
         }
 
         return [
-            'command_line' => $commandLine = implode(' ', $_SERVER['argv']),
+            'command_line' => $commandLine = implode(' ', $_SERVER['argv'] ?? []),
             'identifier' => hash('crc32b', $commandLine.$_SERVER['REQUEST_TIME_FLOAT']),
         ];
     }