PHP函数返回'；null'；以获取jQuery.ajax调用中的成功方法

我遇到了一个与此问题非常相似的问题：jquery json函数返回null。

然而，我遵循了上面包含的建议，因此仍然看到null。

这是我的代码：

JS:

Gallery.prototype.getImages = function(opt){
  var self = this;
      var baseurl = 'http://local.gallery.dev'
  $.ajax({
    url: baseurl+='/controllers/ajax.php',
    type: 'POST',
    contentType: 'application/json; charset=utf-8',
    data: {action : opt},
    dataType: 'JSON',
    success: function(data){
        //self.setImages(data);
        console.log(data)
    },
    error: function(){
        console.log('NOPE');
    }
  });
}

PHP:

class ajax_controller {
function __construct(){
    if(isset($_POST['action']) && !empty($_POST['action'])) {
        $action = $_POST['action'];
        switch($action) {
            case 'Newborn' : $this->Newborn();
                break;
        }
    }
}
/*
 * Process Newborn Gallery request.
 */
public function Newborn(){
    header('Content-type: application/json');
    echo json_encode(array(
      'images/gallery/albums/newborn/kylie/thumbnail/kylie-album.jpg',
      'images/gallery/albums/newborn/payton/thumbnail/payton-1-thumbnail.png'
    ));
}
}

控制台/调试器/网络面板都在说我与ajax控制器的对话是正确的，然而，success方法的data只返回null。

我是PHP的新手，任何建议都非常感谢。

谢谢Ken

更新

我的呼叫仍然返回null，所以我想把我的标题粘贴在这里。

Request URL:http://local.sunnyrose.dev/controllers/ajax.php
Request Method:POST
Status Code:200 OK
Request Headersview source
Accept:application/json, text/javascript, */*; q=0.01
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Connection:keep-alive
Content-Length:14
Content-Type:application/json; charset=UTF-8
Host:local.sunnyrose.dev
Origin:http://local.sunnyrose.dev
Referer:http://local.sunnyrose.dev/
User-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/535.11 (KHTML,              
like Gecko) Chrome/17.0.963.56 Safari/535.11
X-Requested-With:XMLHttpRequest
Request Payload
action=Newborn
Response Headersview source
Connection:Keep-Alive
Content-Length:0
Content-Type:application/json
Date:Mon, 05 Mar 2012 17:49:53 GMT
Keep-Alive:timeout=5, max=92
Server:Apache/2.2.14 (Unix) DAV/2 mod_ssl/2.2.14 OpenSSL/0.9.8l PHP/5.3.1 mod_perl/2.0.4       
Perl/v5.10.1
X-Powered-By:PHP/5.3.1