Simplify property memoization for Flyweight pattern by replacing it with ??=

Author: zonuexe

src/Type/Regex/RegexGroupParser.php

@@ -53,10 +53,8 @@ public function __construct(
 
 	public function parseGroups(string $regex): ?RegexAstWalkResult
 	{
-		if (self::$parser === null) {
-			/** @throws void */
-			self::$parser = Llk::load(new Read(__DIR__ . '/../../../resources/RegexGrammar.pp'));
-		}
+		/** @throws void */
+		self::$parser ??= Llk::load(new Read(__DIR__ . '/../../../resources/RegexGrammar.pp'));
 
 		try {
 			Strings::match('', $regex);