added regression test

Author: staabm

tests/PHPStan/Analyser/nsrt/bug-13214.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace Bug13214;
+
+use function PHPStan\Testing\assertType;
+use stdClass;
+
+class HelloWorld
+{
+	/**
+	 * @param ArrayAccess<int, ?object> $array
+	 */
+	public function sayHello(ArrayAccess $array): void
+	{
+		$child = new stdClass();
+
+		assert($array[1] === null);
+
+		assertType('null', $array[1]);
+
+		$array[1] = $child;
+
+		assertType(stdClass::class, $array[1]);
+	}
+
+	/**
+	 * @param array<int, ?object> $array
+	 */
+	public function sayHelloArray(array $array): void
+	{
+		$child = new stdClass();
+
+		assert(($array[1] ?? null) === null);
+
+		assertType('object|null', $array[1]);
+
+		$array[1] = $child;
+
+		assertType(stdClass::class, $array[1]);
+	}
+}