Fix #6

Allows records to have an empty domain name.

Author: trowski

src/Decoder/Decoder.php

@@ -259,10 +259,6 @@ private function decodeDomainName(DecodingContext $decodingContext, DomainName $
             }
         }
 
-        if (!$labels) {
-            throw new \UnexpectedValueException('Decode error: Empty domain name at position ' . $startIndex);
-        }
-
         $result = [];
         foreach ($labels as $label) {
             if (is_int($label[0])) {

src/Records/Types/DomainName.php

@@ -83,7 +83,9 @@ public function getLabels($tldFirst = false)
     public function setLabels(array $labels, $tldFirst = false)
     {
         if (!$labels) {
-            throw new \InvalidArgumentException('Label list is not a valid domain name: List is empty');
+            $this->labels = [];
+            $this->value = '';
+            return;
         }
 
         $length = $count = 0;