null?报错

这里是HTML部分代码：

<div role="main" class="ui-content">
<form method="post" action="php/login.php" id="form" name="form">
<ul>
<input id="user" type="text" name="user" value="" placeholder="请输入用户名" />
<br>
<input id="password" name="password" type="password" value="" placeholder="请输入密码"/>
<br>
<a id="btn1" type="submit" data-role="button" data-icon="user" 
style="width:30%;float:left">登录</a>
<a data-role="button" data-icon="plus" style="width:30%;float:right">注册</a>
<li id="confirm"></li>
</ul>
</div>

下面是Jquery Ajax代码：

$(document).ready(function(){
    $("#form").submit(function(){
        login();
        return false;
    });
});
function login(){
    var user = $("#user").val();
    var password = $("#password").val();
    if (user == ""){
        $("#confirm").text("请输入登录用户名");
        $("user").focus();
        return false;
    }
    if(password == ""){
        $("#confirm").text("请输入登录密码");
        $("#password").focus();
        return false;aaaaa
    }
    $.ajax({
        type: "POST",
        url: "php/login.php",
        dataType: "json",
        data: {"user" : "user", "password": "password"},
        beforeSend: function(){
        $("confirm").text("登录中，请稍候");
        },
        success: function(msg){
            if(msg == "successful"){
                $("#confirm").text("登录成功，欢迎" + user + "回来！正在进入你的空间");
            }else {
                $("#confirm").text("没有此用户或者密码不正确！");
            }
        }
    });
};

<?php
include_once('db.php');
if(isset($_SESSION['user'])){
	echo json_encode(array('result'=>'successful'));
	return;
}


$user=$_GET['user'];
$password=$_GET['password'];

if($user==""){
	echo json_encode(array('result'=>'failed','message'=>'Username or password wrong'));
	return;
	}
if($password==""){
	echo json_encode(array('result'=>'failed','message'=>'Username or password wrong'));
	return;
}

	$link = new mysqli('localhost', $dbuser, $dbpass, $dbname);

    if ($link->connect_error) {
		die("Connection failed: " . $link->connect_error);
	} 

	$sql = "SELECT * FROM `user` WHERE name= '".$user."' and password= '".$password."'";
	$result = $link->query($sql);
	if ($result->num_rows > 0) {
			$details = $result->fetch_assoc();
			
			$_SESSION['user'] = $details['name'];
			
			echo json_encode(array('result'=>'successful'));
			return;
		}else
		{
			echo json_encode(array('result'=>'failed','message'=>'Username or password wrong'));
			
		}

?>