public function register($name, $handler)
    {
        Assert::string($name, 'The handler name must be a string. Got: %s');
        Assert::notEmpty($name, 'The handler name must not be empty.');

        if (!is_object($handler)) {
            Assert::isCallable($handler, 'The handler must be a callable or an object. Got: %s');
        }

        $this->handlers[$name] = $handler;

        if (!$this->selectedHandler) {
            $this->selectedHandler = $name;
        }
    }