Moved process of sluggifying custom slug to a filter

module/Common/src/Validation/SluggerFilter.php

@@ -0,0 +1,31 @@
+<?php
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink\Common\Validation;
+
+use Cocur\Slugify;
+use Zend\Filter\Exception;
+use Zend\Filter\FilterInterface;
+
+class SluggerFilter implements FilterInterface
+{
+    /** @var Slugify\SlugifyInterface */
+    private $slugger;
+
+    public function __construct(?Slugify\SlugifyInterface $slugger = null)
+    {
+        $this->slugger = $slugger ?: new Slugify\Slugify(['lowercase' => false]);
+    }
+
+    /**
+     * Returns the result of filtering $value
+     *
+     * @param  mixed $value
+     * @throws Exception\RuntimeException If filtering $value is impossible
+     * @return mixed
+     */
+    public function filter($value)
+    {
+        return $value ? $this->slugger->slugify($value) : $value;
+    }
+}