如何在不返回NULL的情况下将数据添加到现有JSON文件？

Question

我在将数据添加到现有JSON文件时遇到了问题。脚本第一次运行时它都可以工作，但第二次文件已经存在时，JSON文件会更新，但值为NULL。

PHP for UPLOADING：

$ds          = DIRECTORY_SEPARATOR;

if(isset($_FILES['files'])){
    $errors= array();
    foreach($_FILES['files']['tmp_name'] as $key => $tmp_name ){
        $file_name = $key.$_FILES['files']['name'][$key];
        $file_size =$_FILES['files']['size'][$key];
        $file_tmp =$_FILES['files']['tmp_name'][$key];
        $file_type=$_FILES['files']['type'][$key];  
        if($file_size > 10097152){
            $errors[]='File size must be less than 10 MB';
        }

        if(empty($errors)==true){

            $dirPath = $ds .'hidden' . $ds .$_SESSION['user']['username']. date('d-m-Y-H-i-s'). $ds;
            $result = mkdir($dirPath, 0770, true);

            move_uploaded_file($file_tmp, $dirPath.$file_name);
            save_document_info_json($file);

        }else{
                print_r($errors);
        }
    }



    if(empty($error)){
        echo "Success";
    }
}

JSON SAVING FILE

function save_document_info_json($file){

   $ds          = DIRECTORY_SEPARATOR;

   $jsonfile = UPLOADEDFILES."docinfo.json";

   if(is_file($jsonfile)){
      $jsonText = file_get_contents($jsonfile);
      $workflow = json_decode($jsonText, true);
   } else{
      $jsonText = '{"statistics": {"total": 0, "approved": 0}, "fileInfo":[]}';
      $workflow = json_decode($jsonText, true);
   }


   for ($i = 0; $i <= count($workflow["fileInfo"]); ++$i){
        $filename = $_FILES['files']['name'][$i];
        $filesize = $_FILES['files']['size'][$i];
        $filetype = $_FILES['files']['type'][$i];
    }

    $fileInfo["status"] = "pending";
    $fileInfo["submittedBy"] = $_SESSION['user']['username'];
    $fileInfo["approvedBy"] = "";

    $fileInfo["fileName"] = $filename;
    $fileInfo["location"] = $ds .'hidden' . $ds .$_SESSION['user']['username']. date('d-m-Y-H-i-s'). $ds;
    $fileInfo["fileType"] = $filetype;
    $fileInfo["size"] = $filesize;

    array_push($workflow["fileInfo"], $fileInfo);
    $total =  count($workflow["fileInfo"]);
    $workflow["statistics"]["total"] = $total;
    file_put_contents($jsonfile, json_encode($workflow));
}