Warning (2): Invalid argument supplied for foreach() [APP/Plugin/Destinations/Controller/DestinationsController.php, line 2310]

    function getDefaultMap($map){
        $mapa = json_decode($map);
        foreach($mapa as $key => $val){

$map = ''
$mapa = null

DestinationsController::getDefaultMap() - APP/Plugin/Destinations/Controller/DestinationsController.php, line 2310
DestinationsController::mapa() - APP/Plugin/Destinations/Controller/DestinationsController.php, line 1598
ReflectionMethod::invokeArgs() - [internal], line ??
Controller::invokeAction() - APP/cakephp/2.5.7/lib/Cake/Controller/Controller.php, line 490
Dispatcher::_invoke() - APP/cakephp/2.5.7/lib/Cake/Routing/Dispatcher.php, line 193
Dispatcher::dispatch() - APP/cakephp/2.5.7/lib/Cake/Routing/Dispatcher.php, line 167
[main] - APP/webroot/index.php, line 117