[CLEANUP] Return null from DeclarationBlock::parse() on failure

Part of #1176.

Author: JakeQZ

config/phpstan-baseline.neon

@@ -48,12 +48,6 @@ parameters:
 			count: 1
 			path: ../src/RuleSet/DeclarationBlock.php
 
-		-
-			message: '#^Returning false in non return bool class method\. Use null with type\|null instead or add bool return type$#'
-			identifier: typePerfect.nullOverFalse
-			count: 1
-			path: ../src/RuleSet/DeclarationBlock.php
-
 		-
 			message: '#^Only booleans are allowed in a negated boolean, string\|null given\.$#'
 			identifier: booleanNot.exprNotBoolean

src/RuleSet/DeclarationBlock.php

@@ -30,14 +30,12 @@ class DeclarationBlock extends RuleSet
     private $selectors = [];
 
     /**
-     * @return DeclarationBlock|false
-     *
      * @throws UnexpectedTokenException
      * @throws UnexpectedEOFException
      *
      * @internal since V8.8.0
      */
-    public static function parse(ParserState $parserState, ?CSSList $list = null)
+    public static function parse(ParserState $parserState, ?CSSList $list = null): ?DeclarationBlock
     {
         $comments = [];
         $result = new DeclarationBlock($parserState->currentLine());
@@ -63,7 +61,7 @@ public static function parse(ParserState $parserState, ?CSSList $list = null)
                 if (!$parserState->comes('}')) {
                     $parserState->consumeUntil('}', false, true);
                 }
-                return false;
+                return null;
             } else {
                 throw $e;
             }