从字符串转换后，json_decode添加NULL

Question

我有以下课程：

class Config
{

    public static $config;
public static function load() {
      $connection = new DBConnection();
      try {
        $sql = 'SELECT `json`
                FROM `general`
                WHERE `title` = "config"
                LIMIT 1';
        $stmt = $connection->dbh->prepare($sql);
        $stmt->execute();
        self::$config = $stmt->fetch(PDO::FETCH_ASSOC);
      } catch (PDOException $e) {
        echo $e->getMessage();
        echo $e->getTraceAsString();
      }
      $connection->disconnect();
      self::$config = json_decode(self::$config['json'], true);
    }
  }

我从数据库中检索到的信息是一种表示JSON的字符串格式。

在我使用json_decode将$ config从STRING转换为ARRAY之后，它在没有任何原因的情况下向数组的末尾添加了另一个“ NULL”单元格...

我试图在类外对变量$ config进行解码，并将其返回而没有“ NULL”。但是我希望它在类本身中执行解码。

存储的JSON：

{
  "settings": {
    "general": {
      "web_name": "WEBSITE",
      "url": "website.com",
      "max_login_attempts": 3,
      "login_block_time": 15,
      "errors_mode": true,
      "time_zone": "",
      "max_events": 35,
      "max_notifications": 35
    },
    "email": {
      "host": "smtp-relay.gmail.com",
      "port": 587,
      "username": "",
      "password": ""
    },
    "vars": {
      "general": {
        "web_name": "[web_name]",
        "url": "[web_url]",
        "max_login_attempts": "[max_login_attempts]",
        "login_block_time": "[login_block_time]"
      },
      "dynamic": {
        "admin_full_name": "[admin_full_name]",
        "admin_email_address": "[admin_email_address]",
        "admin_username": "[admin_username]",
        "admin_id": "[admin_id]",
        "admin_login_attempt_ip": "[admin_login_attempt_ip]"
      }
    }
  }
}

错误的结果（数组的var_dump）-如果难以阅读，请先查看此后的代码：

array(1) { 
    ["settings"]=> array(5) { 
        ["general"]=> array(8) {
             ["web_name"]=> string(7) "WEBSITE" 
             ["url"]=> string(11) "website.com" 
             ["max_login_attempts"]=> int(3) 
             ["login_block_time"]=> int(15) 
             ["errors_mode"]=> bool(true) 
             ["time_zone"]=> string(0) "" 
             ["max_events"]=> int(35) 
             ["max_notifications"]=> int(35) 
        } 
        ["email"]=> array(4) { 
            ["host"]=> string(20) "smtp-relay.gmail.com" 
            ["port"]=> int(587) 
            ["username"]=> string(0) "" 
            ["password"]=> string(0) ""
        }
        ["vars"]=> array(2) { 
            ["general"]=> array(4) { 
                ["web_name"]=> string(10) "[web_name]" 
                ["url"]=> string(9) "[web_url]" 
                ["max_login_attempts"]=> string(20) "[max_login_attempts]" 
                ["login_block_time"]=> string(18) "[login_block_time]" 
            } 
            ["dynamic"]=> array(5) { 
                ["admin_full_name"]=> string(17) "[admin_full_name]" 
                ["admin_email_address"]=> string(21) "[admin_email_address]" 
                ["admin_username"]=> string(16) "[admin_username]" 
                ["admin_id"]=> string(10) "[admin_id]" 
                ["admin_login_attempt_ip"]=> string(24) "[admin_login_attempt_ip]" 
            } 
        } 
        [""]=> NULL 
    } 
}

在对数组进行json_encode后的错误结果（为方便起见）

{
  "settings": {
    "general": {
      "web_name": "WEBSITE",
      "url": "website.com",
      "max_login_attempts": 3,
      "login_block_time": 15,
      "errors_mode": true,
      "time_zone": "",
      "max_events": 35,
      "max_notifications": 35
    },
    "email": {
      "host": "smtp-relay.gmail.com",
      "port": 587,
      "username": "",
      "password": ""
    },
    "vars": {
      "general": {
        "web_name": "[web_name]",
        "url": "[web_url]",
        "max_login_attempts": "[max_login_attempts]",
        "login_block_time": "[login_block_time]"
      },
      "dynamic": {
        "admin_full_name": "[admin_full_name]",
        "admin_email_address": "[admin_email_address]",
        "admin_username": "[admin_username]",
        "admin_id": "[admin_id]",
        "admin_login_attempt_ip": "[admin_login_attempt_ip]"
      }
    },
    "": null **// --> Where does it come from???**
  }
}