Add non regression test

Author: VincentLanglet

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -926,6 +926,11 @@ public function testBug3747(): void
 		$this->analyse([__DIR__ . '/data/bug-3747.php'], []);
 	}
 
+	public function testBug4809(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-4809.php'], []);
+	}
+
 	public function testBug8372(): void
 	{
 		$this->checkExplicitMixed = true;

tests/PHPStan/Rules/Arrays/data/bug-4809.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types = 1);
+
+namespace Bug4809;
+
+class SomeClass
+{
+	/**
+	 * @param array{
+	 *     some?: string,
+	 *     another?: string,
+	 * } $data
+	 * @param string $key
+	 * @return void
+	 */
+	public function someFunction(array $data, string $key): void
+	{
+		if($key !== 'some' && $key !== 'another') {
+			return;
+		}
+
+		if(!array_key_exists($key, $data)) {
+			return;
+		}
+
+		var_dump($data[$key]);
+	}
+}