Unable to stub without overriding function about kahlan HOT 5 CLOSED

    class MyClass
    {
        private function getString(): string
        {
            return "the string";
        }

        public function useString(): string
        {
            return $this->getString();
        }
    }

    describe('without explicit return value', function () {
        beforeEach(function () {
            allow(MyClass::class)->toReceive("getString");
            $myClass = new MyClass();
            $this->result = $myClass->useString();
        });

        it('returns the string', function () {
            expect(MyClass::class)->toReceive("getString")->once();
        });

        it('returns the string', function () {
            expect($this->result)->toBe("the string");
        });
    });

MyClass->getString()
  without explicit return value
    ✖ it returns the string
      an uncaught exception has been thrown in `src/MyClass.php` line 7
      
      message:`TypeError` Code(0) with message "KahlanStub\\MyClass::getString(): Return value must be of type string, null returned"
      
        [NA] - src/MyClass.php, line  to 7
        KahlanStub\MyClass::getString() - src/MyClass.php, line 13
        KahlanStub\MyClass::useString() - spec/MyClass.spec.php, line 10