laravel/framework — pull request #6567 by mrofi (2014-12-03 16:16:09+00:00)
Title: 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.