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    <h3>Editing: DefaultValueResolver.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier &lt;fabien@symfony.com&gt;
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\HttpKernel\Controller\ArgumentResolver;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpKernel\Controller\ArgumentValueResolverInterface;
use Symfony\Component\HttpKernel\ControllerMetadata\ArgumentMetadata;

/**
 * Yields the default value defined in the action signature when no value has been given.
 *
 * @author Iltar van der Berg &lt;kjarli@gmail.com&gt;
 */
final class DefaultValueResolver implements ArgumentValueResolverInterface
{
    /**
     * {@inheritdoc}
     */
    public function supports(Request $request, ArgumentMetadata $argument): bool
    {
        return $argument-&gt;hasDefaultValue() || (null !== $argument-&gt;getType() &amp;&amp; $argument-&gt;isNullable() &amp;&amp; !$argument-&gt;isVariadic());
    }

    /**
     * {@inheritdoc}
     */
    public function resolve(Request $request, ArgumentMetadata $argument): iterable
    {
        yield $argument-&gt;hasDefaultValue() ? $argument-&gt;getDefaultValue() : null;
    }
}
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