Why catch error "NullPointerException" in SQLite select?

Question

I am using sqlite select in asynctask, and the catch error is "NullPointerException". But I cannot figure out why. This is my second table and I completely followed the format of my first table. The first table works, but this one doesn't. What if there are more than one result meet the select condition? How can I make sure each return value could connect to the following xml code? Asynctask class code:

protected class tryconnect extends AsyncTask<Void,Integer,Void>{

    EditText city=(EditText)findViewById(R.id.city_address);
    String   mycity=city.getText().toString();
    EditText street=(EditText)findViewById(R.id.street_address);
    String   mystreet=street.getText().toString();
    EditText postcode=(EditText)findViewById(R.id.postcode_address);
    String   mypostcode=postcode.getText().toString();
    EditText number=(EditText)findViewById(R.id.number_address);
    String   mynumber=number.getText().toString();
    String   ReservedState="Free";


    @Override
    protected Void doInBackground(Void... arg0) {
        try{
            String result=dbHelper1.select1(ReservedState, mycity, mystreet, mypostcode);
        }catch(Exception e){
            e.printStackTrace();
        }


        // TODO Auto-generated method stub
        String baseURL="https://fontys.nedapparking.com/so.xml?Ln=adminfontys&Pw=f0nty589&Cm=1&Fm=A&PrkLt=1&Bay=";
        //c is the retrieving result from reservation table
        String a="1";
        StringBuilder URL=new StringBuilder(baseURL);
        URL.append(a);
        String fullURL=URL.toString();
        try{
            URL website=new URL(fullURL);
            //getting xmlreader to parse data
            SAXParserFactory spf=SAXParserFactory.newInstance();
            SAXParser sp=spf.newSAXParser();
            XMLReader xr=sp.getXMLReader();

            HandlingXMLStuff doingWork=new HandlingXMLStuff();
            xr.setContentHandler(doingWork);
            try{
                xr.parse(new InputSource(website.openStream()));
            }catch(Exception e){
                e.printStackTrace();
            }
            information=doingWork.getInformation();
        }catch(Exception e){
            e.printStackTrace();
        }
        return null;
    }
    protected void onPostExecute(Void result) {
        // TODO Auto-generated method stub
        Message.message(FragmentHandler.this,information);
    }
}

select code in another class:`public String select1 (String ReservedState, String mycity, String mystreet, String mypostcode){

ReservedState="Free";

SQLiteDatabase Database1=dbHelper1.getWritableDatabase();

String[] columns={DbHelper1.KEY_ID1,DbHelper1.KEY_RESERVEDSTATE, DbHelper1.KEY_GEOGRAPHICALLOCATION,DbHelper1.KEY_CITY,DbHelper1.KEY_POSTCODE,DbHelper1.KEY_STREET};

Cursor cursor=Database1.query(DbHelper1.TABLE_NAME1,columns, DbHelper1.KEY_RESERVEDSTATE+"='"+ReservedState+"' AND "+DbHelper1.KEY_CITY+"='"+mycity+"' AND "+DbHelper1.KEY_POSTCODE+"='"+mypostcode+"' AND "+DbHelper1.KEY_STREET+"='"+mystreet+"'",null,null,null,null);

StringBuffer buffer=new StringBuffer();

while(cursor.moveToNext()){

int index1=cursor.getColumnIndex(DbHelper1.KEY_ID1);

int index2=cursor.getColumnIndex(DbHelper1.KEY_RESERVEDSTATE);

int index3=cursor.getColumnIndex(DbHelper1.KEY_GEOGRAPHICALLOCATION);

int index4=cursor.getColumnIndex(DbHelper1.KEY_CITY);

int index5=cursor.getColumnIndex(DbHelper1.KEY_POSTCODE);

int index6=cursor.getColumnIndex(DbHelper1.KEY_STREET);

String id=cursor.getString(index1);

buffer.append(id);

}

return buffer.toString();

}`

And my sqliteassethelper class is as following:

static class DbHelper1 extends SQLiteAssetHelper{
    public static final String KEY_ID1="ID";
    public static final String KEY_RESERVEDSTATE="ReservedState";
    public static final String KEY_GEOGRAPHICALLOCATION="GeographicalLocation";
    public static final String KEY_CITY="City";
    public static final String KEY_POSTCODE="Postcode";
    public static final String KEY_STREET="Street";

    private static String DATABASE_NAME="clientdatabase.db";
    private static final String TABLE_NAME1="ReservedStatus";
    private static final int DATABASE_VERSION1=1;

    public static final String DROP_TABLE="DROP TABLE IF EXISTS "+TABLE_NAME1;
    private Context context;
    private String db_path;

public DbHelper1(Context context){
    super(context,DATABASE_NAME,null,DATABASE_VERSION1);
    //this.DATABASE_NAME=DATABASE_NAME;
    //this.context=context;
    //db_path="/data/data/"+context.getPackageName()+"/databases/";

}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    //delete table
    db.execSQL(DROP_TABLE);
    onCreate(db);

    }