android bluetooth activation error

Question

I am trying to activate bluetooth programatically in android and the application installs fine, but when I click the button to activate BT , it gives exception. I am not able to handle the exception. Any help is greatly appreciated. I am new to this. Here is the code :

package com.example.helloandroid2;


import java.io.IOException;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class HelloAndroid extends Activity {
 // Declare our Views, so we can access them later

 private Button activate_buletooth;
    static final int REQUEST_ENABLE_BT = 0;
    Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
    BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Set Activity Layout
        setContentView(R.layout.main);

         activate_buletooth = (Button)findViewById(R.id.activate_buletooth);

        // Set Click Listener

            activate_buletooth.setOnClickListener(new OnClickListener() {
         @Override
         public void onClick(View v){
          if (mBluetoothAdapter == null) {
              // Device does not support Bluetooth
           Context context = getApplicationContext();
           CharSequence text = "BT not suported";
           int duration = Toast.LENGTH_SHORT;

           Toast toast = Toast.makeText(context, text, duration);
           toast.show();
          }     
          if (!mBluetoothAdapter.isEnabled()) {
              Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
              startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
          }

          // startActivityForResult(discoverableIntent, REQUEST_ENABLE_BT);

         }
        });

    }
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data)
    {
     if(requestCode == REQUEST_ENABLE_BT)
        {
      if(resultCode == RESULT_CANCELED)
            {
       Context context = getApplicationContext();
       CharSequence text = "bt not available";
       int duration = Toast.LENGTH_SHORT;

       Toast toast = Toast.makeText(context, text, duration);
       toast.show();
            }
       else
             {

             }
        }
    }
}