diff --git a/UPGRADE-5.2.md b/UPGRADE-5.2.md
new file mode 100644
index 000000000000..f3a204fcce33
--- /dev/null
+++ b/UPGRADE-5.2.md
@@ -0,0 +1,30 @@
+UPGRADE FROM 5.1 to 5.2
+=======================
+
+Validator
+---------
+
+ * Deprecated the `allowEmptyString` option of the `Length` constraint.
+
+   Before:
+
+   ```php
+   use Symfony\Component\Validator\Constraints as Assert;
+
+   /**
+    * @Assert\Length(min=5, allowEmptyString=true)
+    */
+   ```
+
+   After:
+
+   ```php
+   use Symfony\Component\Validator\Constraints as Assert;
+
+   /**
+    * @Assert\AtLeastOneOf({
+    *     @Assert\Blank(),
+    *     @Assert\Length(min=5)
+    * })
+    */
+   ```
diff --git a/UPGRADE-6.0.md b/UPGRADE-6.0.md
index 1d8243eff7d8..0e3449d80bb9 100644
--- a/UPGRADE-6.0.md
+++ b/UPGRADE-6.0.md
@@ -115,6 +115,34 @@ Security
  * Removed `DefaultLogoutSuccessHandler` in favor of `DefaultLogoutListener`.
  * Added a `logout(Request $request, Response $response, TokenInterface $token)` method to the `RememberMeServicesInterface`.
 
+Validator
+---------
+
+ * Removed the `allowEmptyString` option from the `Length` constraint.
+
+   Before:
+
+   ```php
+   use Symfony\Component\Validator\Constraints as Assert;
+
+   /**
+    * @Assert\Length(min=5, allowEmptyString=true)
+    */
+   ```
+
+   After:
+
+   ```php
+   use Symfony\Component\Validator\Constraints as Assert;
+
+   /**
+    * @Assert\AtLeastOneOf({
+    *     @Assert\Blank(),
+    *     @Assert\Length(min=5)
+    * })
+    */
+   ```
+
 Yaml
 ----
 
diff --git a/src/Symfony/Bridge/Doctrine/Tests/Fixtures/DoctrineLoaderEntity.php b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/DoctrineLoaderEntity.php
index 8c0b348e3bf3..d6aee2d18b0b 100644
--- a/src/Symfony/Bridge/Doctrine/Tests/Fixtures/DoctrineLoaderEntity.php
+++ b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/DoctrineLoaderEntity.php
@@ -36,13 +36,13 @@ class DoctrineLoaderEntity extends DoctrineLoaderParentEntity
 
     /**
      * @ORM\Column(length=20)
-     * @Assert\Length(min=5, allowEmptyString=true)
+     * @Assert\Length(min=5)
      */
     public $mergedMaxLength;
 
     /**
      * @ORM\Column(length=20)
-     * @Assert\Length(min=1, max=10, allowEmptyString=true)
+     * @Assert\Length(min=1, max=10)
      */
     public $alreadyMappedMaxLength;
 
diff --git a/src/Symfony/Bridge/Doctrine/Tests/Resources/validator/BaseUser.xml b/src/Symfony/Bridge/Doctrine/Tests/Resources/validator/BaseUser.xml
index 40b7a138d437..bf64b92ca484 100644
--- a/src/Symfony/Bridge/Doctrine/Tests/Resources/validator/BaseUser.xml
+++ b/src/Symfony/Bridge/Doctrine/Tests/Resources/validator/BaseUser.xml
@@ -13,7 +13,6 @@
                 <option name="min">2</option>
                 <option name="max">120</option>
                 <option name="groups">Registration</option>
-                <option name="allowEmptyString">true</option>
             </constraint>
         </property>
     </class>
diff --git a/src/Symfony/Component/Form/Tests/Extension/Validator/Type/FormTypeValidatorExtensionTest.php b/src/Symfony/Component/Form/Tests/Extension/Validator/Type/FormTypeValidatorExtensionTest.php
index 598687e1a260..4c90cc6316db 100644
--- a/src/Symfony/Component/Form/Tests/Extension/Validator/Type/FormTypeValidatorExtensionTest.php
+++ b/src/Symfony/Component/Form/Tests/Extension/Validator/Type/FormTypeValidatorExtensionTest.php
@@ -67,7 +67,7 @@ public function testGroupSequenceWithConstraintsOption()
             ->create(FormTypeTest::TESTED_TYPE, null, (['validation_groups' => new GroupSequence(['First', 'Second'])]))
             ->add('field', TextTypeTest::TESTED_TYPE, [
                 'constraints' => [
-                    new Length(['min' => 10, 'allowEmptyString' => true, 'groups' => ['First']]),
+                    new Length(['min' => 10, 'groups' => ['First']]),
                     new NotBlank(['groups' => ['Second']]),
                 ],
             ])
@@ -83,8 +83,6 @@ public function testGroupSequenceWithConstraintsOption()
 
     public function testManyFieldsGroupSequenceWithConstraintsOption()
     {
-        $allowEmptyString = property_exists(Length::class, 'allowEmptyString') ? ['allowEmptyString' => true] : [];
-
         $formMetadata = new ClassMetadata(Form::class);
         $authorMetadata = (new ClassMetadata(Author::class))
             ->addPropertyConstraint('firstName', new NotBlank(['groups' => 'Second']))
@@ -116,7 +114,7 @@ public function testManyFieldsGroupSequenceWithConstraintsOption()
             ->add('firstName', TextTypeTest::TESTED_TYPE)
             ->add('lastName', TextTypeTest::TESTED_TYPE, [
                 'constraints' => [
-                    new Length(['min' => 10, 'groups' => ['First']] + $allowEmptyString),
+                    new Length(['min' => 10, 'groups' => ['First']]),
                 ],
             ])
             ->add('australian', TextTypeTest::TESTED_TYPE, [
diff --git a/src/Symfony/Component/Form/Tests/Extension/Validator/ValidatorExtensionTest.php b/src/Symfony/Component/Form/Tests/Extension/Validator/ValidatorExtensionTest.php
index 383b7556d51b..cb9b93abdbf6 100644
--- a/src/Symfony/Component/Form/Tests/Extension/Validator/ValidatorExtensionTest.php
+++ b/src/Symfony/Component/Form/Tests/Extension/Validator/ValidatorExtensionTest.php
@@ -94,13 +94,11 @@ public function testFieldConstraintsInvalidateFormIfFieldIsSubmitted()
 
     public function testFieldsValidateInSequence()
     {
-        $allowEmptyString = property_exists(Length::class, 'allowEmptyString') ? ['allowEmptyString' => true] : [];
-
         $form = $this->createForm(FormType::class, null, [
             'validation_groups' => new GroupSequence(['group1', 'group2']),
         ])
             ->add('foo', TextType::class, [
-                'constraints' => [new Length(['min' => 10, 'groups' => ['group1']] + $allowEmptyString)],
+                'constraints' => [new Length(['min' => 10, 'groups' => ['group1']])],
             ])
             ->add('bar', TextType::class, [
                 'constraints' => [new NotBlank(['groups' => ['group2']])],
@@ -117,16 +115,14 @@ public function testFieldsValidateInSequence()
 
     public function testFieldsValidateInSequenceWithNestedGroupsArray()
     {
-        $allowEmptyString = property_exists(Length::class, 'allowEmptyString') ? ['allowEmptyString' => true] : [];
-
         $form = $this->createForm(FormType::class, null, [
             'validation_groups' => new GroupSequence([['group1', 'group2'], 'group3']),
         ])
             ->add('foo', TextType::class, [
-                'constraints' => [new Length(['min' => 10, 'groups' => ['group1']] + $allowEmptyString)],
+                'constraints' => [new Length(['min' => 10, 'groups' => ['group1']])],
             ])
             ->add('bar', TextType::class, [
-                'constraints' => [new Length(['min' => 10, 'groups' => ['group2']] + $allowEmptyString)],
+                'constraints' => [new Length(['min' => 10, 'groups' => ['group2']])],
             ])
             ->add('baz', TextType::class, [
                 'constraints' => [new NotBlank(['groups' => ['group3']])],
diff --git a/src/Symfony/Component/Form/Tests/Extension/Validator/ValidatorTypeGuesserTest.php b/src/Symfony/Component/Form/Tests/Extension/Validator/ValidatorTypeGuesserTest.php
index e96c8b60c392..2b50c7cc2f06 100644
--- a/src/Symfony/Component/Form/Tests/Extension/Validator/ValidatorTypeGuesserTest.php
+++ b/src/Symfony/Component/Form/Tests/Extension/Validator/ValidatorTypeGuesserTest.php
@@ -66,7 +66,7 @@ public function guessRequiredProvider()
             [new NotNull(), new ValueGuess(true, Guess::HIGH_CONFIDENCE)],
             [new NotBlank(), new ValueGuess(true, Guess::HIGH_CONFIDENCE)],
             [new IsTrue(), new ValueGuess(true, Guess::HIGH_CONFIDENCE)],
-            [new Length(['min' => 10, 'max' => 10, 'allowEmptyString' => true]), new ValueGuess(false, Guess::LOW_CONFIDENCE)],
+            [new Length(['min' => 10, 'max' => 10]), new ValueGuess(false, Guess::LOW_CONFIDENCE)],
             [new Range(['min' => 1, 'max' => 20]), new ValueGuess(false, Guess::LOW_CONFIDENCE)],
         ];
     }
@@ -102,7 +102,7 @@ public function testGuessMaxLengthForConstraintWithMaxValue()
 
     public function testGuessMaxLengthForConstraintWithMinValue()
     {
-        $constraint = new Length(['min' => '2', 'allowEmptyString' => true]);
+        $constraint = new Length(['min' => '2']);
 
         $result = $this->guesser->guessMaxLengthForConstraint($constraint);
         $this->assertNull($result);
diff --git a/src/Symfony/Component/Validator/CHANGELOG.md b/src/Symfony/Component/Validator/CHANGELOG.md
index 9921ef6d4b49..df48d15b3ffe 100644
--- a/src/Symfony/Component/Validator/CHANGELOG.md
+++ b/src/Symfony/Component/Validator/CHANGELOG.md
@@ -1,6 +1,34 @@
 CHANGELOG
 =========
 
+5.2.0
+-----
+
+ * deprecated the `allowEmptyString` option of the `Length` constraint
+
+   Before:
+
+   ```php
+   use Symfony\Component\Validator\Constraints as Assert;
+
+   /**
+    * @Assert\Length(min=5, allowEmptyString=true)
+    */
+   ```
+
+   After:
+
+   ```php
+   use Symfony\Component\Validator\Constraints as Assert;
+
+   /**
+    * @Assert\AtLeastOneOf({
+    *     @Assert\Blank(),
+    *     @Assert\Length(min=5)
+    * })
+    */
+   ```
+
 5.1.0
 -----
 
diff --git a/src/Symfony/Component/Validator/Constraints/Length.php b/src/Symfony/Component/Validator/Constraints/Length.php
index d3404277bef0..3daebf8ff198 100644
--- a/src/Symfony/Component/Validator/Constraints/Length.php
+++ b/src/Symfony/Component/Validator/Constraints/Length.php
@@ -64,5 +64,9 @@ public function __construct($options = null)
         if (null !== $this->normalizer && !\is_callable($this->normalizer)) {
             throw new InvalidArgumentException(sprintf('The "normalizer" option must be a valid callable ("%s" given).', get_debug_type($this->normalizer)));
         }
+
+        if (isset($options['allowEmptyString'])) {
+            trigger_deprecation('symfony/validator', '5.2', sprintf('The "allowEmptyString" option of the "%s" constraint is deprecated.', self::class));
+        }
     }
 }
diff --git a/src/Symfony/Component/Validator/Tests/Constraints/LengthTest.php b/src/Symfony/Component/Validator/Tests/Constraints/LengthTest.php
index b0caef17c9e3..c1c9d60d8bba 100644
--- a/src/Symfony/Component/Validator/Tests/Constraints/LengthTest.php
+++ b/src/Symfony/Component/Validator/Tests/Constraints/LengthTest.php
@@ -12,6 +12,7 @@
 namespace Symfony\Component\Validator\Tests\Constraints;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Bridge\PhpUnit\ExpectDeprecationTrait;
 use Symfony\Component\Validator\Constraints\Length;
 
 /**
@@ -19,6 +20,8 @@
  */
 class LengthTest extends TestCase
 {
+    use ExpectDeprecationTrait;
+
     public function testNormalizerCanBeSet()
     {
         $length = new Length(['min' => 0, 'max' => 10, 'normalizer' => 'trim']);
@@ -39,4 +42,23 @@ public function testInvalidNormalizerObjectThrowsException()
         $this->expectExceptionMessage('The "normalizer" option must be a valid callable ("stdClass" given).');
         new Length(['min' => 0, 'max' => 10, 'normalizer' => new \stdClass()]);
     }
+
+    /**
+     * @group legacy
+     * @dataProvider allowEmptyStringOptionData
+     */
+    public function testDeprecatedAllowEmptyStringOption(bool $value)
+    {
+        $this->expectDeprecation('Since symfony/validator 5.2: The "allowEmptyString" option of the "Symfony\Component\Validator\Constraints\Length" constraint is deprecated.');
+
+        new Length(['allowEmptyString' => $value, 'max' => 5]);
+    }
+
+    public function allowEmptyStringOptionData()
+    {
+        return [
+            [true],
+            [false],
+        ];
+    }
 }
diff --git a/src/Symfony/Component/Validator/Tests/Constraints/LengthValidatorTest.php b/src/Symfony/Component/Validator/Tests/Constraints/LengthValidatorTest.php
index d7969afc565e..584f1e4ae3c8 100644
--- a/src/Symfony/Component/Validator/Tests/Constraints/LengthValidatorTest.php
+++ b/src/Symfony/Component/Validator/Tests/Constraints/LengthValidatorTest.php
@@ -29,6 +29,9 @@ public function testNullIsValid()
         $this->assertNoViolation();
     }
 
+    /**
+     * @group legacy
+     */
     public function testAllowEmptyString()
     {
         $this->validator->validate('', new Length(['value' => 6, 'allowEmptyString' => true]));
diff --git a/src/Symfony/Component/Validator/composer.json b/src/Symfony/Component/Validator/composer.json
index ad9a81eaba8a..9e2a5f752bd5 100644
--- a/src/Symfony/Component/Validator/composer.json
+++ b/src/Symfony/Component/Validator/composer.json
@@ -17,6 +17,7 @@
     ],
     "require": {
         "php": ">=7.2.5",
+        "symfony/deprecation-contracts": "^2.1",
         "symfony/polyfill-ctype": "~1.8",
         "symfony/polyfill-mbstring": "~1.0",
         "symfony/polyfill-php80": "^1.15",

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