adding is_object() in  findClosure() method

Return of method findClosure() is Closure Object that is callable and must be an object. So only using is_callabel() function isn't enough. A string could be callable, example when you adding alias 'app' in your route.
Route::get('apps', array('as' => 'app', function()
{
//
})); will make an error.

change is_object to ($value instanceOf \Closure)

we just need $value instanceOf Closure;