diff --git a/src/Symfony/Component/DependencyInjection/Dumper/XmlDumper.php b/src/Symfony/Component/DependencyInjection/Dumper/XmlDumper.php
index 8017fc579aaa2..17cf2c1a74a68 100644
--- a/src/Symfony/Component/DependencyInjection/Dumper/XmlDumper.php
+++ b/src/Symfony/Component/DependencyInjection/Dumper/XmlDumper.php
@@ -138,7 +138,7 @@ private function addService(Definition $definition, ?string $id, \DOMElement $pa
                 $tag = $this->document->createElement('tag');
                 $tag->setAttribute('name', $name);
                 foreach ($attributes as $key => $value) {
-                    $tag->setAttribute($key, $value);
+                    $tag->setAttribute($key, $value ?? '');
                 }
                 $service->appendChild($tag);
             }
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/containers/container9.php b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/containers/container9.php
index 3ea49503e9753..f4606815cd705 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/containers/container9.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/containers/container9.php
@@ -17,6 +17,7 @@
     ->register('foo', FooClass::class)
     ->addTag('foo', ['foo' => 'foo'])
     ->addTag('foo', ['bar' => 'bar', 'baz' => 'baz'])
+    ->addTag('nullable', ['bar' => 'bar', 'baz' => null])
     ->setFactory(['Bar\\FooClass', 'getInstance'])
     ->setArguments(['foo', new Reference('foo.baz'), ['%foo%' => 'foo is %foo%', 'foobar' => '%foo%'], true, new Reference('service_container')])
     ->setProperties(['foo' => 'bar', 'moo' => new Reference('foo.baz'), 'qux' => ['%foo%' => 'foo is %foo%', 'foobar' => '%foo%']])
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/services9.xml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/services9.xml
index 55ec20ee10059..13fb730237136 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/services9.xml
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/services9.xml
@@ -10,6 +10,7 @@
     <service id="foo" class="Bar\FooClass" public="true">
       <tag name="foo" foo="foo"/>
       <tag name="foo" bar="bar" baz="baz"/>
+      <tag name="nullable" bar="bar" baz=""/>
       <argument>foo</argument>
       <argument type="service" id="foo.baz"/>
       <argument type="collection">
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services9.yml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services9.yml
index fd2be046f8cd6..f9f987e8546cc 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services9.yml
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/services9.yml
@@ -13,6 +13,7 @@ services:
         tags:
             - { name: foo, foo: foo }
             - { name: foo, bar: bar, baz: baz }
+            - { name: nullable, bar: bar, baz: ~ }
         arguments: [foo, '@foo.baz', { '%foo%': 'foo is %foo%', foobar: '%foo%' }, true, '@service_container']
         properties: { foo: bar, moo: '@foo.baz', qux: { '%foo%': 'foo is %foo%', foobar: '%foo%' } }
         calls: