diff --git a/DependencyInjection/Factory/Resolver/AwsS3ResolverFactory.php b/DependencyInjection/Factory/Resolver/AwsS3ResolverFactory.php
index 29976cd34..75991911d 100644
--- a/DependencyInjection/Factory/Resolver/AwsS3ResolverFactory.php
+++ b/DependencyInjection/Factory/Resolver/AwsS3ResolverFactory.php
@@ -92,7 +92,7 @@ public function addConfiguration(ArrayNodeDefinition $builder)
                     ->cannotBeEmpty()
                 ->end()
                 ->scalarNode('cache_prefix')
-                    ->defaultValue(null)
+                    ->defaultValue('')
                 ->end()
                 ->arrayNode('client_config')
                     ->isRequired()
diff --git a/DependencyInjection/Factory/Resolver/FlysystemResolverFactory.php b/DependencyInjection/Factory/Resolver/FlysystemResolverFactory.php
index 76e542bc7..f6090aba1 100644
--- a/DependencyInjection/Factory/Resolver/FlysystemResolverFactory.php
+++ b/DependencyInjection/Factory/Resolver/FlysystemResolverFactory.php
@@ -49,7 +49,7 @@ public function addConfiguration(ArrayNodeDefinition $builder)
                     ->cannotBeEmpty()
                 ->end()
                 ->scalarNode('cache_prefix')
-                    ->defaultValue(null)
+                    ->defaultValue('')
                 ->end()
                 ->scalarNode('root_url')
                     ->isRequired()
diff --git a/Tests/DependencyInjection/Factory/Resolver/AwsS3ResolverFactoryTest.php b/Tests/DependencyInjection/Factory/Resolver/AwsS3ResolverFactoryTest.php
index 10d4677ab..19f4d7a08 100644
--- a/Tests/DependencyInjection/Factory/Resolver/AwsS3ResolverFactoryTest.php
+++ b/Tests/DependencyInjection/Factory/Resolver/AwsS3ResolverFactoryTest.php
@@ -431,7 +431,7 @@ public function testAddDefaultOptionsIfNotSetOnAddConfiguration(): void
         $this->assertSame([], $config['get_options']);
 
         $this->assertArrayHasKey('cache_prefix', $config);
-        $this->assertNull($config['cache_prefix']);
+        $this->assertSame('', $config['cache_prefix']);
     }
 
     public function testSupportAwsV3ClientConfig(): void