MVC3 - Value cannot be null or empty. Parameter name: contentType

I am currently using Steven Sanderson book Pro ASP.NET MVC 2 Framework. But I am using MVC 3 framwork. This question is related to my previous question. I am getting the following error...

Value cannot be null or empty. Parameter name: contentType pointing at line...

return File(product.Picture1, product.ImageMimeType);.

In the book he says...

We don’t want either of these properties to be directly visible in the product-editing UI. We can use [ScaffoldColumn(false)] to exclude ImageMimeType from the automatically generated UI. We don’t need to give any hints about ImageData because ASP.NET MVC’s built-in object editor template won’t scaffold byte[] properties anyway—it only scaffolds properties of “simple” types like string, int, and DateTime.5.

So I have done that and still getting the same error message? If possible how could this be solved.

Index.cshtml

@foreach (var item in Model) 
<td>
      <img src="@Url.Action("GetImage", "ProductCategoryL2", new { id =  
      @item.SubProductCategoryID })" alt="" height="100" width="100" /> 
    </td>

Edit.cshtml

@using (Html.BeginForm("ProductCategoryL2", "GetImage", FormMethod.Post, 
new { @enctype = "multipart/form-data" }))
{
  <div class="editor-field">
     <img src="@Url.Action("GetImage", "ProductCategoryL2", new { id = 
      @Model.SubProd开发者_开发技巧uctCategoryID })" alt="" /> 
      @Html.ValidationMessage("Picture1", "*")
     <input type="file" name="Image" size="23"/>
  </div>
}

cs file

public FileContentResult GetImage(int id)
    {
        var product = db.SubProductCategory2.First(x => 
        x.SubProductCategoryID == id);
        return File(product.Picture1, product.ImageMimeType); //Value cannot be null or empty. Parameter name: contentType 
    }

another cs file

   [ScaffoldColumn(false)]
   public string ImageMimeType { get; set; }

I have setup the field for ImageMimeType in the SQL Server 2008R2 exactly same was as in the book. I am using VS 2010 ASP.NET 4.0 MVC3. Thanks in advance. Table name is SubProductCategory2.

Put in a break point in the method and inspect the value of product.ImageMimeType. I think you'll find that it's either null or an empty string. Either it's not being retrieved from the database or the database doesn't contain anything in the column.