Android - Database - length=0; index=5

hello world :D how are you

I need to know what is the problem with this code??

    public String getLastDate(){
        SQLiteDatabase database = lecturesDB.getReadableDatabase();
        try {
            String [] a = {DATE};
            Cursor cursor = database.query(LECTURES_TABLE, a, null, null, null, null, null);
            int i = cursor.getColumnIndex(DATE);
            cursor.moveToFirst();
            String ld = cursor.getString(i);//Thu, 26 Mar 2015 17:19:56
            DateFormat format = new SimpleDateFormat("dd MMM yyyy hh:mm:ss ");
            Date date = format.parse(ld.substring(5));
            while (cursor.moveToNext()){
                String c = cursor.getString(i);
                Log.e("Mayiaz",ld+"    "+c);
                if (format.parse(c.substring(5)).getTime()>date.getTime()){
                    date = format.parse(c.substring(5));
                    ld = c;
                }
            }
            return ld;
        }catch (Exception e) {Log.e("Mayiaz",e.getMessage());return "";}
        finally {
            database.close();
        }
    }

its return "" and the exception show this message : "04-04 19:55:45.702 1478-1634/com.mine.rbt E/Mayiaz﹕ length=0; index=5"

and thanks :)