空指针异常

Question

public class IUserDao { public boolean find(String name,String password) throws Exception{  Connection conn = null;  PreparedStatement st = null;         ResultSet rs =null;          try{            conn = DbUtils.getConn();            String sql = "select * from User where name=? and password=?";            st = conn.prepareStatement(sql);            st.setString(1, name);            st.setString(2, password);            rs = st.executeQuery();           }catch (Exception e) {                     }          System.out.println(rs); if(rs.next()){ System.out.println("没有记录"); return false; } else{ System.out.println("登录成功"); return true; } } public static void main(String args[]) throws Exception{ IUserDao ud=new IUserDao(); ud.find("admin", "12345d6"); } }其他类调用这个find 方法时，java.lang.NullPointerException at dao.IUserDao.find(IUserDao.java:36)    ...    ....