3.0 update hasError() - fix#4563

This pull request is related to #4563.

When validating file the 
```php
errors =
 [	'name' => null,
	'tmp_name' => null,
	'error' => null,
	'type' => null,
	'size' => null
]]);
```

This causes FormHelper to add a `div` with class `error` ans the 5 empty `<li>` has shown on the bug report.
please use `!== null` instead