Merge pull request #5 from tvlooy/empty_html

avoid warning that html is empty

Author: tvlooy

src/CssFromHTMLExtractor.php

@@ -86,7 +86,9 @@ protected function createDomDocumentFromHtml($html)
     {
         $document = new \DOMDocument('1.0', 'UTF-8');
         $internalErrors = libxml_use_internal_errors(true);
-        $document->loadHTML(mb_convert_encoding($html, 'HTML-ENTITIES', 'UTF-8'));
+        if (!empty($html)) {
+            $document->loadHTML(mb_convert_encoding($html, 'HTML-ENTITIES', 'UTF-8'));
+        }
         libxml_use_internal_errors($internalErrors);
         $document->formatOutput = true;