Fixed issue with ArrayAccess stub

stubs/ArrayObject.stub

@@ -20,7 +20,7 @@ interface ArrayAccess
 	public function offsetGet($offset);
 
 	/**
-	 * @param TKey $offset
+	 * @param TKey|null $offset
 	 * @param TValue $value
 	 * @return void
 	 */

tests/PHPStan/Rules/Arrays/OffsetAccessAssignmentRuleTest.php

@@ -121,4 +121,10 @@ public function testInheritDocTemplateTypeResolution(): void
 		$this->analyse([__DIR__ . '/data/inherit-doc-template-type-resolution.php'], []);
 	}
 
+	public function testAssignNewOffsetToStubbedClass(): void
+	{
+		$this->checkUnionTypes = true;
+		$this->analyse([__DIR__ . '/data/new-offset-stub.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Arrays/data/new-offset-stub.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace NewOffsetStub;
+
+/**
+ * @phpstan-implements \ArrayAccess<int, \stdClass>
+ */
+abstract class Foo implements \ArrayAccess
+{
+
+}
+
+function (Foo $foo): void {
+	$foo[] = new \stdClass();
+};

tests/PHPStan/Rules/Methods/data/bug-2950.php

@@ -100,7 +100,7 @@ public function offsetGet($offset): float
 	}
 
 	/**
-	 * @param int   $offset
+	 * @param int|null   $offset
 	 * @param float $value
 	 */
 	public function offsetSet($offset, $value): void