fix: not checking an empty value is the role of “NotBlank”

Author: Maxime Leclercq

src/Validator/Constraints/YoutubeUrlValidator.php

@@ -29,6 +29,10 @@ public function validate(mixed $value, Constraint $constraint): void
 
         $value = (string) $value;
 
+        if ('' === $value) {
+            return;
+        }
+
         if (!preg_match(self::YOUTUBE_REGEX_VALIDATOR, $value)) {
             $this->context->buildViolation($constraint->message)
                 ->setParameter('{{ string }}', $value)