<?php

class A {
  public function hello() {
    return 'hello';
  }
}

class B {
}

class C extends B {
  /** @var A|null */
  public $foo;
}

$maybe_c = rand(0, 10) ? new C() : new B();

if (!$maybe_c instanceof C || !$maybe_c->foo) {
  throw new \Exception('OK');
}

echo $maybe_c->foo->hello(); 

if (!$maybe_c instanceof C) {
  throw new \Exception('OK');
}

if (!$maybe_c->foo) {
  throw new \Exception('OK');
}

echo $maybe_c->foo->hello();