private function initActionTypeExtensions()
    {
        $this->actionTypeExtensions = [];

        foreach ($this->loadActionTypeExtensions() as $extension) {
            if (!$extension instanceof ActionTypeExtensionInterface) {
                throw new UnexpectedTypeException($extension, ActionTypeExtensionInterface::class);
            }

            $type = $extension->getExtendedType();

            $this->actionTypeExtensions[$type][] = $extension;
        }
    }