C# Textfield Null Reference Exception

Hi everyone I'm working on a version of Save and Load from XML U3 Collections where the _playername is typed in. But I keep getting a null reference exception and it tells me that the null reference is coming from the textfield. I'm not sure how to fix it. Any idea what is up?

 using UnityEngine; 
 using System.Collections; 
 using System.Xml; 
 using System.Xml.Serialization; 
 using System.IO; 
 using System.Text; 
  
 public class _GameSaveLoad: MonoBehaviour { 
  
 
    Rect _Save, _Load, _SaveMSG, _LoadMSG; 
    bool _ShouldSave, _ShouldLoad,_SwitchSave,_SwitchLoad; 
    string _FileLocation,_FileName; 
    public GameObject _Player; 
    UserData myData; 
    string _PlayerName; 
    string _data; 
  
    Vector3 VPosition; 

    void Start () { 

       _Save=new Rect(10,80,100,20); 
       _Load=new Rect(10,100,100,20); 
       _SaveMSG=new Rect(10,120,400,40); 
       _LoadMSG=new Rect(10,140,400,40); 
  
       _FileLocation=Application.dataPath; 
       _FileName="SaveData.xml"; 
  

  
       myData=new UserData(); 
    } 
  
    void Update () {} 
  
    void OnGUI() 
    {

//null reference exception

_PlayerName = GUILayout.TextField (_PlayerName,GUILayout.Width(150), GUILayout.Height(25));

    if (GUI.Button(_Load,"Load")) { 
  
       GUI.Label(_LoadMSG,"Loading from: "+_FileLocation); 
      
       LoadXML(); 
       if(_data.ToString() != "") 
       { 
         myData = (UserData)DeserializeObject(_data); 
         VPosition=new Vector3(myData._iUser.x,myData._iUser.y,myData._iUser.z);              
         _Player.transform.position=VPosition;  
         Debug.Log(myData._iUser.name); 
       } 
  
    }   
    if (GUI.Button(_Save,"Save")) { 
  
      GUI.Label(_SaveMSG,"Saving to: "+_FileLocation); 
      myData._iUser.x=_Player.transform.position.x; 
      myData._iUser.y=_Player.transform.position.y; 
      myData._iUser.z=_Player.transform.position.z; 
      myData._iUser.name=_PlayerName;     
      _data = SerializeObject(myData); 
 
      CreateXML(); 
      Debug.Log(_data); 
    } 
  
  
    } 
  
    string UTF8ByteArrayToString(byte[] characters) 
    {      
       UTF8Encoding encoding = new UTF8Encoding(); 
       string constructedString = encoding.GetString(characters); 
       return (constructedString); 
    } 
  
    byte[] StringToUTF8ByteArray(string pXmlString) 
    { 
       UTF8Encoding encoding = new UTF8Encoding(); 
       byte[] byteArray = encoding.GetBytes(pXmlString); 
       return byteArray; 
    } 
  

    string SerializeObject(object pObject) 
    { 
       string XmlizedString = null; 
       MemoryStream memoryStream = new MemoryStream(); 
       XmlSerializer xs = new XmlSerializer(typeof(UserData)); 
       XmlTextWriter xmlTextWriter = new XmlTextWriter(memoryStream, Encoding.UTF8); 
       xs.Serialize(xmlTextWriter, pObject); 
       memoryStream = (MemoryStream)xmlTextWriter.BaseStream; 
       XmlizedString = UTF8ByteArrayToString(memoryStream.ToArray()); 
       return XmlizedString; 
    } 
  
   
    object DeserializeObject(string pXmlizedString) 
    { 
       XmlSerializer xs = new XmlSerializer(typeof(UserData)); 
       MemoryStream memoryStream = new MemoryStream(StringToUTF8ByteArray(pXmlizedString)); 
       XmlTextWriter xmlTextWriter = new XmlTextWriter(memoryStream, Encoding.UTF8); 
       return xs.Deserialize(memoryStream); 
    } 
    void CreateXML() 
    { 
       StreamWriter writer; 
       FileInfo t = new FileInfo(_FileLocation+"\\"+ _FileName); 
       if(!t.Exists) 
       { 
          writer = t.CreateText(); 
       } 
       else 
       { 
          t.Delete(); 
          writer = t.CreateText(); 
       } 
       writer.Write(_data); 
       writer.Close(); 
       Debug.Log("File written."); 
    } 
  
    void LoadXML() 
    { 
       StreamReader r = File.OpenText(_FileLocation+"\\"+ _FileName); 
       string _info = r.ReadToEnd(); 
       r.Close(); 
       _data=_info; 
       Debug.Log("File Read"); 
    } 
 } 
  

  public class UserData 
  { 
 
    public DemoData _iUser; 
 
    public UserData() { } 
   
    public struct DemoData 
    { 
       public float x; 
       public float y; 
       public float z; 
       public string name;
       
    } 
 }