SplObjectStorage's ArrayAccess will never return null

stubs/SplObjectStorage.stub

@@ -61,4 +61,10 @@ class SplObjectStorage implements Countable, Iterator, Serializable, ArrayAccess
      */
     public function setInfo($data): void { }
 
+    /**
+     * @param TObject $offset
+     * @return TData
+     */
+    public function offsetGet($offset);
+
 }

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -10767,6 +10767,11 @@ public function dataBug4504(): array
 		return $this->gatherAssertTypes(__DIR__ . '/data/bug-4504.php');
 	}
 
+	public function dataBug4436(): array
+	{
+		return $this->gatherAssertTypes(__DIR__ . '/data/bug-4436.php');
+	}
+
 	/**
 	 * @param string $file
 	 * @return array<string, mixed[]>
@@ -10982,6 +10987,7 @@ private function gatherAssertTypes(string $file): array
 	 * @dataProvider dataCompact
 	 * @dataProvider dataBug4500
 	 * @dataProvider dataBug4504
+	 * @dataProvider dataBug4436
 	 * @param string $assertType
 	 * @param string $file
 	 * @param mixed ...$args

tests/PHPStan/Analyser/data/bug-4436.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace Bug4436;
+
+use function PHPStan\Analyser\assertType;
+
+class Bar
+{
+}
+
+class Foo
+{
+	/** @var \SplObjectStorage<Bar, string> */
+	private \SplObjectStorage $storage;
+
+	public function __construct()
+	{
+		$this->storage = new \SplObjectStorage();
+	}
+
+	public function add(Bar $bar, string $value): void
+	{
+		$this->storage[$bar] = $value;
+	}
+
+	public function get(Bar $bar): string
+	{
+		assertType('string', $this->storage[$bar]);
+		return $this->storage[$bar];
+	}
+}