diff --git a/src/Symfony/Component/HttpFoundation/InputBag.php b/src/Symfony/Component/HttpFoundation/InputBag.php
index b2aff595c492..c83d63d6d520 100644
--- a/src/Symfony/Component/HttpFoundation/InputBag.php
+++ b/src/Symfony/Component/HttpFoundation/InputBag.php
@@ -72,12 +72,12 @@ public function add(array $inputs = [])
     /**
      * Sets an input by name.
      *
-     * @param string|array $value
+     * @param string|array|null $value
      */
     public function set(string $key, $value)
     {
-        if (!is_scalar($value) && !\is_array($value) && !method_exists($value, '__toString')) {
-            trigger_deprecation('symfony/http-foundation', '5.1', 'Passing "%s" as a 2nd Argument to "%s()" is deprecated, pass a string or an array instead.', get_debug_type($value), __METHOD__);
+        if (null !== $value && !is_scalar($value) && !\is_array($value) && !method_exists($value, '__toString')) {
+            trigger_deprecation('symfony/http-foundation', '5.1', 'Passing "%s" as a 2nd Argument to "%s()" is deprecated, pass a string, array, or null instead.', get_debug_type($value), __METHOD__);
         }
 
         $this->parameters[$key] = $value;
diff --git a/src/Symfony/Component/HttpFoundation/Tests/InputBagTest.php b/src/Symfony/Component/HttpFoundation/Tests/InputBagTest.php
index bd6f3114d7eb..870057e41bdb 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/InputBagTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/InputBagTest.php
@@ -51,7 +51,7 @@ public function testFilterArray()
     public function testSetWithNonStringishOrArrayIsDeprecated()
     {
         $bag = new InputBag();
-        $this->expectDeprecation('Since symfony/http-foundation 5.1: Passing "Symfony\Component\HttpFoundation\InputBag" as a 2nd Argument to "Symfony\Component\HttpFoundation\InputBag::set()" is deprecated, pass a string or an array instead.');
+        $this->expectDeprecation('Since symfony/http-foundation 5.1: Passing "Symfony\Component\HttpFoundation\InputBag" as a 2nd Argument to "Symfony\Component\HttpFoundation\InputBag::set()" is deprecated, pass a string, array, or null instead.');
         $bag->set('foo', new InputBag());
     }