Added regression test

Author: staabm

tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php

@@ -1232,4 +1232,18 @@ public function testBug1O580(): void
 		]);
 	}
 
+	public function testBug4443(): void
+	{
+		if (PHP_VERSION_ID < 80000) {
+			$this->markTestSkipped('Test requires PHP 8.0.');
+		}
+
+		$this->analyse([__DIR__ . '/data/bug-4443.php'], [
+			[
+				'Method Bug4443\HelloWorld::getArray() should return array<mixed> but returns array<mixed>|null.',
+				22
+			]
+		]);
+	}
+
 }

tests/PHPStan/Rules/Methods/data/bug-4443.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace Bug4443;
+
+class HelloWorld
+{
+	/** @var array<mixed> */
+	private static ?array $arr = null;
+
+	private static function setup(): void
+	{
+		self::$arr = null;
+	}
+
+	/** @return array<mixed> */
+	public static function getArray(): array
+	{
+		if (self::$arr === null) {
+			self::$arr = [];
+			self::setup();
+		}
+		return self::$arr;
+	}
+}
+
+HelloWorld::getArray();