Use getter to access the RuleSet object property

Author: JakeQZ

src/RuleSet/DeclarationBlock.php

@@ -133,7 +133,7 @@ public static function parse(ParserState $parserState, ?CSSList $list = null): ?
         }
         $result->setComments($comments);
 
-        RuleSet::parseRuleSet($parserState, $result->ruleSet);
+        RuleSet::parseRuleSet($parserState, $result->getRuleSet());
 
         return $result;
     }