Runtime Exception in Android SQLlite onCreate

I am just trying to make connection of my Android App with the database and insert some values in it. But I am getting Runtime Exception

**06-12 01:02:47.847: E/AndroidRuntime(27848): FATAL EXCEPTION: main
  06-12 01:02:47.847: E/AndroidRuntime(27848): Process:   com.example.database,PID: 27848
06-12 01:02:47.847: E/AndroidRuntime(27848): java.lang.NullPointerException
06-12 01:02:47.847: E/AndroidRuntime(27848):    at  com.example.database.DataBaseManager.onCreate(DataBaseManager.java:38)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:252)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at com.example.database.MainActivity$1.onClick(MainActivity.java:31)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at android.view.View.performClick(View.java:4640)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at android.view.View$PerformClick.run(View.java:19421)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at android.os.Handler.handleCallback(Handler.java:733)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at android.os.Handler.dispatchMessage(Handler.java:95)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at android.os.Looper.loop(Looper.java:146)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at android.app.ActivityThread.main(ActivityThread.java:5602)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at java.lang.reflect.Method.invokeNative(Native Method)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at java.lang.reflect.Method.invoke(Method.java:515)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
06-12 01:02:47.847: E/AndroidRuntime(27848):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)

This is my code: DataBaseManager.java public class DataBaseManager extends SQLiteOpenHelper {

public static String DATABASE_NAME="First DB";
public static String TABLE_NAME="First table";
public static String COL_FNAME="fname";
public static String COL_LNAME="lname";
public static final String COLUMN_ID = "_id";
private static final String DATABASE_CREATE = "create table First DB"+ "(" +   COLUMN_ID + " integer primary key autoincrement, " + COL_FNAME+ " text ,"+COL_LNAME+"text);";
SQLiteDatabase db;

private static final String DATABASE_CREATE = “create table “ DATABASE_TABLE+ “ (“ + KEY_ID +“ integer primary key autoincrement, “ +KEY_NAME + “ text not null);”;*/


public DataBaseManager(Context context) {
super(context, DATABASE_NAME, null, 1);
// TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase arg0) {
// TODO Auto-generated method stub
db.execSQL("create table First DB " +
"(id integer primary key, fname text,lname text)"
);
}

@Override
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS "+DATABASE_NAME);
onCreate(db);

}
public void insert(SQLiteDatabase ddb,String fname,String lname)
{

ddb.execSQL("insert into     "  +DATABASE_NAME+"values(null,'"+fname+"','"+lname+"');");
}

public void readData() {


// TODO Auto-generated method stub
SQLiteDatabase db=this.getReadableDatabase();
Cursor res=db.rawQuery("select * from"+DATABASE_NAME+";",null);
int rows=res.getCount();
Toast.makeText(null,"now of rows are "+rows+"tillnow",    Toast.LENGTH_LONG).show();

}

MainActivity: public class MainActivity extends ActionBarActivity {

Button insert,read;
DataBaseManager dbm;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
insert=(Button)findViewById(R.id.insert);
read=(Button)findViewById(R.id.read);
dbm=new DataBaseManager(this);
//getWritableDatabase();
insert.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
SQLiteDatabase db=
dbm.getWritableDatabase();
dbm.insert(db,"nikhil", "saxena");
dbm.insert(db,"rahul", "saxena");
dbm.insert(db,"rahul", "dhillon");
dbm.insert(db,"nikhil", "dhillon");
}
});

Please suggest.

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