Unity Null Reference Error

Hello,

I have a unity script (posted below) that connects to a php file which then checks the username and password against a database. However, everytime we click the login button, we get a nullreference error on line 49 which is loginform.addfield

Any help would be greatly appreciated. I have posted both unity code and php code.

 using UnityEngine;
 using System.Collections;
 
 public class Login : MonoBehaviour {
 
  public Texture LoginBackground;
  public Texture2D stylebackground;
  public GUIStyle LoginStyle;
  public GUIStyle LoginTextBox;
  public GUIStyle LoginButton;
  public string Username;
  public string Password;
  public float transparent;
  private string url;
  public WWW w;
  public WWWForm loginform;
  // Use this for initialization
  void Start () {
  LoginStyle.fontSize = 72;
  LoginStyle.alignment = TextAnchor.MiddleCenter;
  LoginTextBox.fontSize = 20;
  LoginTextBox.alignment = TextAnchor.MiddleCenter;
  LoginTextBox.normal.background = stylebackground;
  LoginButton.fontSize = 30;
  LoginButton.alignment = TextAnchor.MiddleCenter;
  url = "http://redlightlife.tk/scripts/checklogin.php";
  }
  
  // Update is called once per frame
  void Update () {
  
  }
  
  void OnGUI() {
  GUI.backgroundColor = Color.black;
  GUI.DrawTexture(new Rect(0,0,Screen.width,Screen.height),LoginBackground,ScaleMode.StretchToFill, false, 0.0f);
  GUI.Label(new Rect(Screen.width/2-250,Screen.height/2-250,500,250),"Username:", LoginStyle);
  Username = GUI.TextField(new Rect(Screen.width/2-250,Screen.height/2-80,500,50), Username, 10, LoginTextBox);
  GUI.Label(new Rect(Screen.width/2-250,Screen.height/2-50,500,250),"Password:", LoginStyle);
  Password = GUI.TextField(new Rect(Screen.width/2-250,Screen.height/2+120,500,50), Password, 10, LoginTextBox);
  if (GUI.Button(new Rect(Screen.width/2-150,Screen.height/2+200,300,50),"Login:", LoginButton))
  {
  CheckLogin();
  }
  }
  
  void CheckLogin()
  {
  loginform.AddField("username", Username);
  loginform.AddField("password", Password);
  w = new WWW(url,loginform);
  Debug.Log("Downloaded");
  if (w.error != null)
  {
  print(w.error);
  }
  else
  {
  print("Login Okay");
  string formText = w.text;
  w.Dispose();
  Debug.Log(formText);
  }
  }
 }

  <?php 
  function main($formUse = true)
  {
 $link = mysql_connect('bondsolutionsnjcom.fatcowmysql.com', 'lightswitch', '*password*'); 
 if (!$link) { 
     die('Could not connect: ' . mysql_error()); 
 } 
 echo 'Connected successfully'; 
 mysql_select_db(red_light_life_accounts1);
 
 // This could be supplied by a user, for example
 $username;
 $password;
 
 if(!$username || !$password) {
 
     echo "Login or password cant be empty.";
 
 } else {
 
     $SQL = "SELECT username,password FROM accounts WHERE username = '" . $username . "' & password = '" . $password . '"';
 
         $result_id = @mysql_query($SQL) or die("DATABASE ERROR!");
 
         $total = mysql_num_rows($result_id);
 
         if($total) {
 
             $datas = @mysql_fetch_array($result_id);
 
             if(!strcmp($pass, $datas["password"])) {
 
                 echo "Success";
 
             } else {
 
                 echo "Username or password is wrong.";
 
             }
 
         } else {
 
             echo "Data invalid - cant find username.";
 
         }
 
     }
  }
 
 // Close mySQL Connection
  
 mysql_close();
 ?>