diff --git a/src/Symfony/Component/Config/Definition/Builder/TreeBuilder.php b/src/Symfony/Component/Config/Definition/Builder/TreeBuilder.php
index 6cb5585a637dc..13a18db3ae1c5 100644
--- a/src/Symfony/Component/Config/Definition/Builder/TreeBuilder.php
+++ b/src/Symfony/Component/Config/Definition/Builder/TreeBuilder.php
@@ -11,7 +11,6 @@
 
 namespace Symfony\Component\Config\Definition\Builder;
 
-use Symfony\Component\Config\Definition\Exception\TreeWithoutRootNodeException;
 use Symfony\Component\Config\Definition\NodeInterface;
 
 /**
@@ -35,10 +34,6 @@ public function __construct(string $name, string $type = 'array', NodeBuilder $b
      */
     public function getRootNode(): NodeDefinition
     {
-        if (null === $this->root) {
-            throw new \RuntimeException(sprintf('Calling %s() before creating the root node is not supported, migrate to the new constructor signature instead.', __METHOD__));
-        }
-
         return $this->root;
     }
 
@@ -51,7 +46,6 @@ public function getRootNode(): NodeDefinition
      */
     public function buildTree()
     {
-        $this->assertTreeHasRootNode();
         if (null !== $this->tree) {
             return $this->tree;
         }
@@ -61,21 +55,9 @@ public function buildTree()
 
     public function setPathSeparator(string $separator)
     {
-        $this->assertTreeHasRootNode();
-
         // unset last built as changing path separator changes all nodes
         $this->tree = null;
 
         $this->root->setPathSeparator($separator);
     }
-
-    /**
-     * @throws \RuntimeException if root node is not defined
-     */
-    private function assertTreeHasRootNode()
-    {
-        if (null === $this->root) {
-            throw new TreeWithoutRootNodeException('The configuration tree has no root node.');
-        }
-    }
 }
diff --git a/src/Symfony/Component/Config/Definition/Exception/TreeWithoutRootNodeException.php b/src/Symfony/Component/Config/Definition/Exception/TreeWithoutRootNodeException.php
deleted file mode 100644
index 67b0c4bb2e084..0000000000000
--- a/src/Symfony/Component/Config/Definition/Exception/TreeWithoutRootNodeException.php
+++ /dev/null
@@ -1,19 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Component\Config\Definition\Exception;
-
-/**
- * @author Roland Franssen <franssen.roland@gmail.com>
- */
-class TreeWithoutRootNodeException extends \RuntimeException
-{
-}
diff --git a/src/Symfony/Component/DependencyInjection/Compiler/ValidateEnvPlaceholdersPass.php b/src/Symfony/Component/DependencyInjection/Compiler/ValidateEnvPlaceholdersPass.php
index 8fd84fac00eeb..be0f1edd201fe 100644
--- a/src/Symfony/Component/DependencyInjection/Compiler/ValidateEnvPlaceholdersPass.php
+++ b/src/Symfony/Component/DependencyInjection/Compiler/ValidateEnvPlaceholdersPass.php
@@ -12,7 +12,6 @@
 namespace Symfony\Component\DependencyInjection\Compiler;
 
 use Symfony\Component\Config\Definition\BaseNode;
-use Symfony\Component\Config\Definition\Exception\TreeWithoutRootNodeException;
 use Symfony\Component\Config\Definition\Processor;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Extension\ConfigurationExtensionInterface;
@@ -80,10 +79,7 @@ public function process(ContainerBuilder $container)
                     continue;
                 }
 
-                try {
-                    $this->extensionConfig[$name] = $processor->processConfiguration($configuration, $config);
-                } catch (TreeWithoutRootNodeException $e) {
-                }
+                $this->extensionConfig[$name] = $processor->processConfiguration($configuration, $config);
             }
         } finally {
             BaseNode::resetPlaceholders();
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Compiler/ValidateEnvPlaceholdersPassTest.php b/src/Symfony/Component/DependencyInjection/Tests/Compiler/ValidateEnvPlaceholdersPassTest.php
index b370c177c87df..84d6d8db82835 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Compiler/ValidateEnvPlaceholdersPassTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Compiler/ValidateEnvPlaceholdersPassTest.php
@@ -14,7 +14,6 @@
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Config\Definition\Builder\TreeBuilder;
 use Symfony\Component\Config\Definition\ConfigurationInterface;
-use Symfony\Component\Config\Definition\Exception\TreeWithoutRootNodeException;
 use Symfony\Component\DependencyInjection\Compiler\MergeExtensionConfigurationPass;
 use Symfony\Component\DependencyInjection\Compiler\RegisterEnvVarProcessorsPass;
 use Symfony\Component\DependencyInjection\Compiler\ValidateEnvPlaceholdersPass;
@@ -274,20 +273,6 @@ public function testEnvWithVariableNode(): void
         $this->assertSame($expected, $container->resolveEnvPlaceholders($ext->getConfig()));
     }
 
-    /**
-     * @group legacy
-     */
-    public function testConfigurationWithoutRootNode(): void
-    {
-        $container = new ContainerBuilder();
-        $container->registerExtension(new EnvExtension(new EnvConfigurationWithoutRootNode()));
-        $container->loadFromExtension('env_extension');
-
-        $this->doProcess($container);
-
-        $this->addToAssertionCount(1);
-    }
-
     public function testEmptyConfigFromMoreThanOneSource()
     {
         $container = new ContainerBuilder();
@@ -386,14 +371,6 @@ public function getConfigTreeBuilder()
     }
 }
 
-class EnvConfigurationWithoutRootNode implements ConfigurationInterface
-{
-    public function getConfigTreeBuilder()
-    {
-        return new TreeBuilder('env_extension');
-    }
-}
-
 class ConfigurationWithArrayNodeRequiringOneElement implements ConfigurationInterface
 {
     public function getConfigTreeBuilder()
@@ -438,11 +415,7 @@ public function load(array $configs, ContainerBuilder $container)
             return;
         }
 
-        try {
-            $this->config = $this->processConfiguration($this->getConfiguration($configs, $container), $configs);
-        } catch (TreeWithoutRootNodeException $e) {
-            $this->config = null;
-        }
+        $this->config = $this->processConfiguration($this->getConfiguration($configs, $container), $configs);
     }
 
     public function getConfig()