Change default $lineNumber to null.

Author: JakeQZ

src/RuleSet/DeclarationBlock.php

@@ -46,9 +46,9 @@ class DeclarationBlock implements CSSElement, CSSListItem, Positionable, RuleCon
     private $ruleSet;
 
     /**
-     * @param int<0, max> $lineNumber
+     * @param int<1, max>|null $lineNumber
      */
-    public function __construct(int $lineNumber = 0)
+    public function __construct(?int $lineNumber = null)
     {
         $this->setPosition($lineNumber);
         $this->ruleSet = new RuleSet($lineNumber);