If no expression can be build, the selector is invalid

Author: JanDC

src/CssFromHTMLExtractor.php

@@ -149,6 +149,10 @@ function (Rule $rule) use ($xPath, $cssIdentifier, $htmlIdentifier) {
 
                 $expression = $this->buildExpressionForSelector($rule->getSelector());
 
+                if (!$expression) {
+                    return false;
+                }
+
                 /** @var DOMNodeList $elements */
                 $elements = $xPath->query($expression);