PHP：难以从json_decode返回所需的值（或数据结构）

I'm using json_decode on this json data here:

issues": [

 {
    "id": "51526",
    "key": "123",
    "fields": {
        "zone": [
            {
                "name": "football",
                "active": true
            },
            {
                "name": "baseball",
                "active": true
            }
        ],
        "icon": {
            "id": "1"
        }
    }
},
{
    "id": "51228",
    "key": "3108",
    "fields": {
        "zone": null,
        "icon": {
            "id": "10"
            }
        }
    }
 ]

}

I can properly extract the name data which will be ["football", "baseball"]. However, I also want to capture the null value from the 2nd data set so my data really looks like

 ["football", "baseball", null].

Basically, I want to look at "zone" and get the value of "name", if "zone" is null then the value is null in order to get this data structure ["football", "baseball", null].

I've tried everything I could think of, but I'm not great at php. Is this possible to do?

Php code:

$decoded_array = json_decode($result)->{'issues'};           
            foreach($decoded_array as $issues){                        
            foreach($issues->{'fields'}->{'zone'} as $zn){  
            $nm[] = $zn->{'name'};           
  }
}

When you iterate the json object, check if "zone" is null. If it is, you can add null in your result array.

Pseudo code:

Iterate jsonObject 
  if (jsonObject["fields"]["zone"] == null)
  then push_in_array(result,null)

You can do something like this:

$data = json_decode($json);
$issues = $data->issues;

$names = array();
foreach($issues as $issue){
  $zones = $issue->fields->zone;
  foreach($zones as $zone){
    if($zone != null){
        $name = $zone->name;
        array_push($names,$name);   
    }else{
        array_push($names,null);
    }
  }      
}