Fatal error when filter contains closure

The profiler serialize objects returned by DataCollectors, but PHP can't serialize Closures. So if on filter is a closure or an object containing closure, we end up with the following error : 
```
Fatal error: Uncaught exception 'Exception' with message 'Serialization of 'Closure' is not allowed' in ...
```

My pull request replace objects passed as callback by the string : "Method **method name** of an object **class name**"