为什么我的ASP.NET FormView总是呈现EmptyTemplate

我有一个FormView绑定到一个放置在用户控件内的ObjectDataSource，用以下代码初始化：

<asp:ObjectDataSource ID="odsCampaign" runat="server"
    DataObjectTypeName="code.model.Campaign"
    TypeName="code.model.Campaign"
    SelectMethod="LoadCampaign">
    <SelectParameters>
        <asp:QueryStringParameter Name="code" QueryStringField="id" Type="Int32" />
    </SelectParameters>
</asp:ObjectDataSource>
<%-- ... --%>
<asp:FormView ID="fvCampaign" runat="server"
    DataSourceID="odsCampaign">
    <EmptyDataTemplate>
        <span>No campaign loaded.</span>
    </EmptyDataTemplate>
    <ItemTemplate>
        <span>Campaign</span>
        <span><%# Eval("Subject") %></span>
        <%-- ... --%>
    </ItemTemplate>
</asp:FormView>

我后面的代码看起来像这样：

// CampaignCallCollection inherits from IEnumerable<CampaignCall>
public class Campaign : CampaignCallCollection
{
    // Some property to show
    public string Subject { get; set; }
    // Constructor
    public Campaign(int code)
        : base()
    {
        // Initialize the object based on the primary key passed to the constructor
        InitializeCampaign(code);
    }
    private void InitializeCampaign(int code)
    {
        // Initialization Code
    }
    // Loading method for ObjectDataSource
    public static Campaign LoadCampaign(int code)
    {
        // Return new instance of an initialized campaign object.
        Campaign oCampaign = new Campaign(code);
        //throw new Exception(oCampaign.Subject);
        return oCampaign;
    }
}

但是，如果我启用了异常，则正确的主题文本将作为异常消息传递。但是我的FormView在所有方面都渲染EmptyTemplate。我真的不认为这里有错。有人能帮我吗？

提前感谢！