Retornando Null de pesquisa no banco de dados MySql

try {       
	Class.forName(Driver);
	Connection conn = DriverManager.getConnection(Local,Usuario,Senha);
	String query = "SELECT  Sum(Saldo) as maior  FROM advo where ID_Clientes ='"+txt_Codigo1.getText()+"' and Retirado= 'Sim'";
        ResultSet rs;
        PreparedStatement pst = conn.prepareStatement(query);
      
        rs = pst.executeQuery();
         
        if(rs.next()==true)
	{
           so = Double.valueOf(rs.getString("maior"));          
        } 
	else
             so=merda;
   
        pst.close();   
        conn.close();
    
    } catch (SQLException ex) {        
        JOptionPane.showMessageDialog(null, "ERRO DE SQL: "+ex);   
    } catch (ClassNotFoundException e) {      
        JOptionPane.showMessageDialog(null, "ERRO DE DRIVER: "+e);  
    }
}