未显示自定义数据类型类

我有一个CustomProductProperty模型，它允许用户为他们的产品拥有自定义字段，其中包含一个CustomDataType模型，该模型链接到处理用户定义的数据类型的数据库。

[Table("Product")]
public class Product
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ProductID { get; set; }
    public int ProductTypeID { get; set; }
    [Display(Name = "Product Name")]
    public string ProductName { get; set; }
    [ForeignKey("ProductTypeID")]
    [Display(Name = "Product Type")]
    public virtual ProductType ProductType { get; set; }
    public virtual ICollection<CustomProductProperty> CustomProperties { get; set; } 
}
[Table("CustomProductProperty")]
public class CustomProductProperty
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int CustomPropertyID { get; set; }
    public int CustomDataTypeID { get; set; }
    [ForeignKey("CustomDataTypeID")]
    public virtual CustomDataType DataType { get; set; }
    public int ProductID { get; set; }
    [ForeignKey("ProductID")]
    public virtual Product Product { get; set; }
    public string PropertyValue { get; set; }
}
[Table("CustomDataType")]
public class CustomDataType
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int CustomTypeID { get; set; }
    public string PropertyName { get; set; }
    public CustomDataTypes DataType { get; set; }
    public int ModuleID { get; set; }
    [ForeignKey("ModuleID")]
    public Module Module { get; set; }
}

当试图在我的视图中显示这一点时，我创建了一个显示模板来处理CustomProductProperty的ICollection<>出于某种原因，DataType.PropertyName是空的，但PropertyValue仍然返回正确的数据，有人知道为什么PropertyName是空的吗?

@model IEnumerable<InventoryManager.Models.CustomProductProperty>
@{
    Layout = null;
}
@foreach (var item in Model)
{
<tr>
    <th>@Html.DisplayFor(model => item.DataType.PropertyName)</th>
    <td>@Html.DisplayFor(model => item.PropertyValue)</td>
</tr>    
}