Fix the difference between ?T and T|null

src/PhpDoc/TypeNodeResolver.php

@@ -384,7 +384,7 @@ private function resolveThisTypeNode(ThisTypeNode $typeNode, NameScope $nameScop
 
 	private function resolveNullableTypeNode(NullableTypeNode $typeNode, NameScope $nameScope): Type
 	{
-		return TypeCombinator::addNull($this->resolve($typeNode->type, $nameScope));
+		return TypeCombinator::union($this->resolve($typeNode->type, $nameScope), new NullType());
 	}
 
 	private function resolveUnionTypeNode(UnionTypeNode $typeNode, NameScope $nameScope): Type

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -786,6 +786,10 @@ public function dataFileAsserts(): iterable
 			yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6591.php');
 		}
 
+		if (PHP_VERSION_ID >= 80000) {
+			yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6790.php');
+		}
+
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6584.php');
 	}
 

tests/PHPStan/Analyser/data/bug-6790.php

@@ -0,0 +1,66 @@
+<?php declare(strict_types = 1); // lint >= 8.0
+
+namespace Bug6790;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @template T
+ */
+class Repository
+{
+	/**
+	 * @param array<T> $items
+	 */
+	public function __construct(private array $items) {}
+
+	/**
+	 * @return ?T
+	 */
+	public function find(string $id)
+	{
+		return $this->items[$id] ?? null;
+	}
+}
+
+/**
+ * @template T
+ */
+class Repository2
+{
+	/**
+	 * @param array<T> $items
+	 */
+	public function __construct(private array $items) {}
+
+	/**
+	 * @return T|null
+	 */
+	public function find(string $id)
+	{
+		return $this->items[$id] ?? null;
+	}
+}
+
+class Foo
+{
+
+	/**
+	 * @param Repository<string> $r
+	 * @return void
+	 */
+	public function doFoo(Repository $r): void
+	{
+		assertType('string|null', $r->find('foo'));
+	}
+
+	/**
+	 * @param Repository2<string> $r
+	 * @return void
+	 */
+	public function doFoo2(Repository2 $r): void
+	{
+		assertType('string|null', $r->find('foo'));
+	}
+
+}