If there's no alias, a `null` should be passed down to reporter. 
This is the only way for the reporter to know that this particular test does not have an alias.

Imagine you have a reporter that creates a HTML document, which includes:
````php
if($testAlias){
   echo "<h2 class=\"aliasName\">$testAlias</h2>";
}
````
Right now it would not be possible (the above code would always run), because you'd be passing on numeric keys.