minor #27915 [DependencyInjection] add missing test for #27710 (xabbuh)

This PR was merged into the 4.1 branch.

Discussion
----------

[DependencyInjection] add missing test for #27710

| Q             | A
| ------------- | ---
| Branch?       | 4.1
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | https://github.com/symfony/symfony/pull/27710#pullrequestreview-131904804
| License       | MIT
| Doc PR        |

Commits
-------

a265caf041 [DependencyInjection] add missing test for #27710

src/Symfony/Component/DependencyInjection/Tests/Compiler/ValidateEnvPlaceholdersPassTest.php

@@ -234,6 +234,18 @@ class ValidateEnvPlaceholdersPassTest extends TestCase
         $this->addToAssertionCount(1);
     }
 
+    public function testEmptyConfigFromMoreThanOneSource()
+    {
+        $container = new ContainerBuilder();
+        $container->registerExtension(new EnvExtension(new ConfigurationWithArrayNodeRequiringOneElement()));
+        $container->loadFromExtension('env_extension', array());
+        $container->loadFromExtension('env_extension', array());
+
+        $this->doProcess($container);
+
+        $this->addToAssertionCount(1);
+    }
+
     public function testDiscardedEnvInConfig(): void
     {
         $container = new ContainerBuilder();
@@ -313,6 +325,24 @@ class EnvConfigurationWithoutRootNode implements ConfigurationInterface
     }
 }
 
+class ConfigurationWithArrayNodeRequiringOneElement implements ConfigurationInterface
+{
+    public function getConfigTreeBuilder()
+    {
+        $treeBuilder = new TreeBuilder();
+        $treeBuilder->root('env_extension')
+            ->children()
+                ->arrayNode('nodes')
+                    ->isRequired()
+                    ->requiresAtLeastOneElement()
+                    ->scalarPrototype()->end()
+                ->end()
+            ->end();
+
+        return $treeBuilder;
+    }
+}
+
 class EnvExtension extends Extension
 {
     private $configuration;
@@ -335,6 +365,10 @@ class EnvExtension extends Extension
 
     public function load(array $configs, ContainerBuilder $container)
     {
+        if (!array_filter($configs)) {
+            return;
+        }
+
         try {
             $this->config = $this->processConfiguration($this->getConfiguration($configs, $container), $configs);
         } catch (TreeWithoutRootNodeException $e) {