Here's a small demo:

https://phpstan.org/r/747de7f4958a04636ecfb3e0b56a47c5

class Foo
{
	/**
	 * @return $this|null
	 */
    public function foo()
    {
        if (rand(0,1) === 1) {
            return $this;
        } else {
            return null;
        }
    }
}

$foo = new Foo();

if (null !== $bar = $foo->foo()) {
    $bar->foo();
}

21 Calling method foo() on possibly null value of type Foo|null.

As you can see, $bar should be of type Foo but PHPStan for some reason thinks that the value may be null. Interestingly, this error message goes away as soon as you remove the doctype.

Is this a known issue?

I've just started using PHPStan yesterday and it's awesome! 🤘 Thank you so much for your hard work!