diff --git a/src/Validator/Constraints/TimeFormatValidator.php b/src/Validator/Constraints/TimeFormatValidator.php
index b6c2cbf7..b8ed544b 100644
--- a/src/Validator/Constraints/TimeFormatValidator.php
+++ b/src/Validator/Constraints/TimeFormatValidator.php
@@ -26,6 +26,10 @@ class TimeFormatValidator extends ConstraintValidator
             throw new UnexpectedTypeException($constraint, __NAMESPACE__ . '\TimeFormat');
         }
 
+        if (null === $value || '' === $value) {
+            return;
+        }
+
         if (!is_scalar($value) && !(\is_object($value) && method_exists($value, '__toString'))) {
             throw new UnexpectedValueException($value, 'string');
         }
diff --git a/tests/Validator/Constraints/TimeFormatValidatorTest.php b/tests/Validator/Constraints/TimeFormatValidatorTest.php
index c7e8d92f..e42d1a77 100644
--- a/tests/Validator/Constraints/TimeFormatValidatorTest.php
+++ b/tests/Validator/Constraints/TimeFormatValidatorTest.php
@@ -44,7 +44,7 @@ class TimeFormatValidatorTest extends ConstraintValidatorTestCase
     /**
      * @dataProvider getValidTimes
      */
-    public function testValidationSucceeds(string $value)
+    public function testValidationSucceeds(?string $value)
     {
         $this->validator->validate($value, new TimeFormat());
         $this->assertNoViolation();
@@ -53,6 +53,8 @@ class TimeFormatValidatorTest extends ConstraintValidatorTestCase
     public function getValidTimes()
     {
         return [
+            [''],
+            [null],
             ['00:00'],
             ['00:01'],
             ['23:00'],
@@ -65,7 +67,7 @@ class TimeFormatValidatorTest extends ConstraintValidatorTestCase
     /**
      * @dataProvider getInvalidTimes
      */
-    public function testValidationProblem(string $value)
+    public function testValidationProblem(?string $value)
     {
         $this->validator->validate($value, new TimeFormat());
 
@@ -78,6 +80,7 @@ class TimeFormatValidatorTest extends ConstraintValidatorTestCase
     public function getInvalidTimes()
     {
         return [
+            ['a'],
             ['1:00'],
             ['01:1'],
             ['00:60'],