Warning: mysqli::real_escape_string(): Couldn't fetch mysqli in /var/www/html/example/includes/classes/class.example.php on line 31 [duplicate]

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• Warning: mysqli_query(): Couldn't fetch mysqli 1 answer

I am getting the following error :

Warning: mysqli::real_escape_string(): Couldn't fetch mysqli in /var/www/html/example/includes/classes/class.example.php on line 31

I checked whether $this->mysqli is object of class mysqli it returns true but still I am getting this error

   <?php

   class changetext
     {
      public $mysqli=null;

      function changetext()
      {
        $this->makeconnection();    
      }
      function makeconnection()
      {
        global $config;
        $this->mysqli=new mysqli( $config['DBHostName'],$config['DBUserName'],$config['DBPassword'],$config['DBName'] );
        if($this->mysqli->connect_errno){
          echo $this->mysqli->connect_error;
          die("could not connect to mysql database");
        }
      }
      function selecttitle($id)
      {
        if((!is_object($this->mysqli) && !get_class($this->mysqli) == 'mysqli') || 
          !($this->mysqli instanceof MySQLi) || !is_a($this->mysqli, 'mysqli')  || $this->mysqli->connect_errno)
        {
                //$this->makeconnection(); //it's not coming here
               echo "shivaaa";die(); 
        }
        echo "class of $this->mysqli : ".get_class($this->mysqli);
        echo "<br>";
        echo "instance of $this->mysqli : ".$this->mysqli instanceof MySQLi;
        $id = $this->mysqli->real_escape_string($id);
      }
  }

Thanks in advance