Test on PHP 8.1

Author: nicolas-grekas

.github/workflows/ci.yaml

@@ -24,6 +24,7 @@ jobs:
                     - '7.3'
                     - '7.4'
                     - '8.0'
+                    - '8.1'
                 dependencies:
                     - 'highest'
                 include:

src/Flex.php

@@ -122,7 +122,7 @@ class_exists(__NAMESPACE__.str_replace('/', '\\', substr($file, \strlen(__DIR__)
         $this->config = $composer->getConfig();
         $this->options = $this->initOptions();
 
-        $symfonyRequire = preg_replace('/\.x$/', '.x-dev', getenv('SYMFONY_REQUIRE') ?: ($composer->getPackage()->getExtra()['symfony']['require'] ?? null));
+        $symfonyRequire = preg_replace('/\.x$/', '.x-dev', getenv('SYMFONY_REQUIRE') ?: ($composer->getPackage()->getExtra()['symfony']['require'] ?? ''));
 
         if ($composer2 = version_compare('2.0.0', PluginInterface::PLUGIN_API_VERSION, '<=')) {
             $rfs = Factory::createHttpDownloader($this->io, $this->config);