don't typecast null values inside dispatcher.php

please review @DeepDiver1975 @Raydiation 

Example code:
```php
	/**
	 * @param int $limit
	 * @param int $offset
	 * @return Response
	 *
	 * @NoAdminRequired
	 * @NoCSRFRequired
	 */
	public function index($limit=null, $offset=null) {
		try {
			var_dump(func_get_args());exit;
```

Output master:
```
array (size=2)
  0 => 0
  1 => 0
```

This branch: 
```text
array (size=2)
  0 => null
  1 => null
```