其中语句 MVC 4 中的可选条件

我有一个模型：

    using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Web;
namespace ReviewLogs.Models
{
    public class SearchModel
    {
        [Display(Name = "Type: ")]
        public int? type { get; set; }
        [Display(Name = "Server: ")]
        public string curServer { get; set; }
        [Display(Name = "Status: ")]
        public string status { get; set; }
        [Display(Name = "User Name: ")]
        public string searchedUser { get; set; }

        [Display(Name = "Month Ending: ")]
        public int? monthEnd { get; set; }
        [Display(Name = "Year Ending: "),
        RegularExpression("^([0-9]{4})$", ErrorMessage = "Year must be entered and a valid 4 digit number")]
        public int? yearEnd { get; set; }
        [Display(Name = "Min Log Date: ")]
        public string minLogDate { get; set; }
        [Display(Name = "Max Log Date: ")]
        public string maxLogDate { get; set; }

        [Display(Name = "Ticket Number: ")]
        public string ticket { get; set; }

        [Display(Name = "Comment: ")]
        public string comment { get; set; }
        public SearchModel()
        {
            searchedUser = " ";
        }
    }
}

A 控制器：

        public ActionResult LogSearch()
        {
            if (Request.IsAuthenticated)
            {
                loadDropDown();
                return View();
            }
            else
            {
                return RedirectToAction("index", "home");
            }
        }
        [HttpPost]
        public ActionResult LogSearch(SearchModel submission)
        {
            loadDropDown();


            return RedirectToAction("NameSearchList", "Search", new { userName = submission.searchedUser ,type = submission.type.Value});

        }
public ActionResult NameSearchList(int? type, string userName = "")
        {

                var cnn = new reviewlogsEntities();
                return View(cnn.logrecords.Where(m => m.username == userName && m.typeid == type));


        }

和观点：

    @model ReviewLogs.Models.SearchModel
@{
    ViewBag.Title = "Add Review";
}
@section Scripts{
    <script src="~/Scripts/jquery-1.12.0.min.js"></script>
    <script src="~/Scripts/datetimepicker_css.js"></script>
    <script src="~/Scripts/CurDropDownChecker.js"></script>
}

}

<h2>Add Review</h2>
@Html.ValidationSummary(true, "Submission Failed, Please Try Again")
<p id="success">@ViewBag.SuccessMessage</p>
<div class="formBody">
    @using (Html.BeginForm())
    {
        <div class="inputOthers">
            @Html.LabelFor(model => model.type)
            @Html.DropDownList("type", ViewBag.type as IEnumerable<SelectListItem>, "", new { onchange = "setDisplay();" })
            @Html.ValidationMessageFor(model => model.type)
        </div>
    <div class="inputOthers">
        @Html.LabelFor(model => model.searchedUser)
        @Html.DropDownList("searchedUser", ViewBag.users as IEnumerable<SelectListItem>, " ")
    </div>
        <div class="inputOthers">
            @Html.LabelFor(model => model.curServer)
            @Html.DropDownList("curServer", ViewBag.server as IEnumerable<SelectListItem>, " ")
        </div>
        <div class="inputOthers">
            @Html.LabelFor(model => model.status)
            @Html.DropDownList("status", ViewBag.status as IEnumerable<SelectListItem>, " ")
        </div>
        <div class="inputOthers">
            @Html.LabelFor(model => model.ticket)
            @Html.TextBoxFor(model => model.ticket)
        </div>
        <div class="inputOthers">
            @Html.LabelFor(model => model.comment)
            @Html.TextAreaFor(model => model.comment, new { style = "width:320px; height: 160px;" })
        </div>
        <div class="inputOthers">
            @Html.LabelFor(model => model.minLogDate)
            @Html.TextBoxFor(model => model.minLogDate, new { @readonly = "readonly" })
            <a href="javascript: NewCssCal('logDate','mmddyyyy','arrow',true,12)">
                <img src="~/Images/cal.gif" width="16" height="16" alt="Pick a date">
            </a>
        </div>
     <div class="inputOthers">
        @Html.LabelFor(model => model.maxLogDate)
        @Html.TextBoxFor(model => model.maxLogDate, new { @readonly = "readonly" })
        <a href="javascript: NewCssCal('logDate','mmddyyyy','arrow',true,12)">
            <img src="~/Images/cal.gif" width="16" height="16" alt="Pick a date">
        </a>
     </div>
        <div class="inputOthers">
            <span id="monthEnd">
                @Html.LabelFor(model => model.monthEnd)
                @Html.DropDownListFor(model => model.monthEnd, ViewBag.months as IEnumerable<SelectListItem>, " ")
            </span>
            <span id="yearEnd">
                @Html.LabelFor(model => model.yearEnd)
                @Html.TextBoxFor(model => model.yearEnd, new { @Value = DateTime.Now.Year })
            </span>

        </div>
        <input class="submitButton" type="submit" value="Submit" style="margin-left:126px;margin-bottom: 20px;" onclick="return confirm('If you would like to submit press OK');" />
    }
</div>

因此，如果您查看此内容，则用户可以输入许多可选字段。如果他们在该字段中输入数据，则将其添加到搜索结果中。现在，如果他们输入类型并搜索用户，它将调出包含相应数据的页面。但是，我试图解决的问题是如果他们不输入类型怎么办。我不希望出现这种搜索。现在它这样做：

http://localhost:51730/Search/NameSearchList?userName=Admin&type=1

但是假设他们不搜索名称，而只搜索类型。如何确保"用户名=管理员"不会出现。我想限制每一个，如果它们没有输入或 NULL，只有输入的那些。

您能否展示一下我将如何制定可选要求的解决方案？

谢谢！