Fix depreciation giving null to mb_strtolower

src/UrlInfo/UrlInfo.php

@@ -213,7 +213,7 @@ class UrlInfo {
      * @return $this
      */
     public function setProtocol (?string $protocol = null): self {
-        $this->protocol = self::ensureNull(mb_strtolower($protocol));
+        $this->protocol = self::ensureNull(mb_strtolower($protocol ?? ''));
         return $this;
     }
 
@@ -241,7 +241,7 @@ class UrlInfo {
      * @return $this
      */
     public function setHost (?string $host = null): self {
-        $this->host = self::ensureNull(mb_strtolower($host));
+        $this->host = self::ensureNull(mb_strtolower($host ?? ''));
         return $this;
     }