关于laravel图片上传ajax的麻烦

显示错误:

在null上调用成员函数getClientOriginalExtension()

这是我的代码

形式:

<form id="regForm" role="form" enctype="multipart/form-data">
                    <input type="hidden" name="_token" value="{{ csrf_token() }}">
                    <div class="box-body">
                        <div class="form-group">
                            <label for="exampleInputEmail1">Title</label>
                            <input type="text" class="form-control" name="title" id="exampleInputEmail1" placeholder="Enter email">
                        </div>
                        <div class="form-group">
                            <label for="exampleInputPassword1">Type</label>
                            <input type="text" class="form-control" id="exampleInputPassword1" placeholder="Password">
                        </div>
                        <div class="form-group">
                            <label for="exampleInputFile">File input</label>
                            <input type="file" name="image" id="exampleInputFile">
                        </div>
                    </div><!-- /.box-body -->
                    <div class="box-footer">
                        <button type="submit" class="btn btn-primary">Submit</button>
                    </div>
                </form>

这是我的ajax脚本

<script type="text/javascript">
    $(document).ready(function(){
        //alert($("#email").val());
    });
    $("#regForm").submit(function(){
        var selector = $(this);
        var form = selector.serializeArray();
        $.ajax({
            url: "{{URL::to('admin/snl_add_post')}}",
            type: "POST",
            data: form,
            dataType: "json",
            success: function(data){
                if(!data.success)
                {
                    $.each(data.errors, function(key, value){
                        selector.find("input[name="+key+"]").attr({"style":"border:1.5px solid red;"});
                    });
                }
                else
                {
                    setTimeout(function(){
                        // Move to a new location or you can do something else
                        window.location.href = "{{URL::to('stickers_and_labels')}}";
                    }, 3000);
                }
            }
        });
        return false;
    });
</script>

和控制器

public function snl_add_post(){
        $response = array();
        $rules = array(
            'title' => 'required'
        );
        $validator = Validator::make(Input::all(), $rules);
        if($validator->fails()){
            $response["errors"] = $validator->messages();
            $response["success"] = FALSE;
            $response["msg"] = "Invalid Inputs";
        }
        else
        {
            $careers = new Careers;
            $careers->title = Input::get('title');
            $destinationPath = 'images/snl/';
            $extension = Input::file('image')->getClientOriginalExtension();
            $fileName = rand(11111,99999).'.'.$extension;
            Input::file('image')->move($destinationPath, $fileName);
            $careers->img_path = 'images/snl/'.$filename;
            $careers->save();
            if($careers){
                $response["success"] = true;
                $response["msg"] = "Success";
            }else{
                $response["success"] = false;
                $response["msg"] = "May error";
            }
        }

        return Response::json($response);
    }

我认为我的错误是在ajax，但我不太确定。