NullPointerException帮小弟我找找异常，纠结死了

      public BasicInf getBasicInf(String staId){          BasicInf BasicInf=null;          try{              ps = connection.prepareStatement("select * from BasicInf where staId=?");              ps.setString(1,staId);              ResultSet rs = ps.executeQuery();              while (rs.next()) {                  System.out.println(rs.getString(1));                  System.out.println(rs.getString(2));                  System.out.println(rs.getString(3));                  System.out.println(rs.getString(4));                                    BasicInf.setStaId(rs.getString(1));                  BasicInf.setBirthday(rs.getString(2));                  BasicInf.setNation(rs.getString(4));                  BasicInf.setSex(rs.getString(3));                  return BasicInf;              }          }catch(Exception e)          {              e.printStackTrace();          }          return BasicInf;      }