docs: public User getUser(String fieldName, String fieldValue){
          Select q = new Select().from(User.class);
          String nameColumn = ModelReflector.instance(User.class).getColumnDescriptor(fieldName).getName();
          q.where(new Expression(q.getPool(),nameColumn,Operator.EQ,new BindVariable(q.getPool(),fieldValue)));
          
          List<? extends User> users  = q.execute(User.class);
          if (users.size() == 1){
              return users.get(0);
          }
          return null;
      }