If equals empty string type coercion

The following code:
```php
$x = function(string $a) {
};
$data = @file_get_contents("non_existing_file");
if ($data == "")
  exit();
$x($data);
```

Produces the following error:

    Parameter #1 $a of closure expects string, string|false given.

But that is not correct as `if ($data == "")` enters for $data = false, thus there is no way that $x is called with false.
