Regression test

Closes phpstan/phpstan#4357

Author: ondrejmirtes

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -618,6 +618,7 @@ public function dataFileAsserts(): iterable
 
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6404.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6399.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-4357.php');
 	}
 
 	/**

tests/PHPStan/Analyser/data/bug-4357.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace Bug4357;
+
+use function PHPStan\Testing\assertType;
+
+class Sample {
+	/** @var null|array<string, string> */
+	private $arr = null;
+
+	public function test(): void {
+		if ($this->arr === null) {
+			return;
+		}
+
+		assertType('array<string, string>', $this->arr);
+
+		unset($this->arr['hello']);
+
+		assertType('array<string, string>', $this->arr);
+
+		if (count($this->arr) === 0) {
+			$this->arr = null;
+		}
+	}
+}