How to show GridView Image conditionally in ASP.Net

Hi all,

For this I am using ASP.NET 4.5, C#, and Entity Framework to SQL.

I have some sections of my site where users can make multiple entries and can optionally upload attachments. There is a page where the user can see a gridview that acts as an overview of the entires. I have been asked to display a column with a paperclip icon if an attachment exists.

The way the database is structured, the table that holds the entries has columns like this:

id, schoolName, dateStarted, dateEnded, attachmentId

The attachments are in another table. For this table the attachmentId will hold an Int32 or be NULL (no attachment). My current query looks like basically like this: 

 var query = context.applications.Where(c => c.id == applicationPrimaryKey);
 var results = result.educationUniversities.ToList();
 gdvEducationUniversity.DataSource = results;
 gdvEducationUniversity.DataBind();

Gridview looks like this:

  <asp:GridView
                            ID="gdvWorkMentor"
                            runat="server"                          
                            AutoGenerateColumns="False"                           
                            DataKeyNames="id"                         
                            <Columns>
                                <asp:BoundField AccessibleHeaderText="Trainee Name" DataField="traineeName" HeaderText="Trainee Name" HtmlEncode="False" />
                                <asp:BoundField AccessibleHeaderText="Employer/Agency" DataField="employerAgency" HeaderText="Employer/Agency" HtmlEncode="False" />
                                <asp:BoundField AccessibleHeaderText="Start Date" DataField="dateStart" HeaderText="Start Date" DataFormatString="{0:MM/dd/yyyy}" />
                                <asp:BoundField AccessibleHeaderText="End Date" DataField="dateEnd" HeaderText="End Date" DataFormatString="{0:MM/dd/yyyy}" />

                                <asp:ButtonField AccessibleHeaderText="View/Edit" CommandName="view" HeaderText="View/Edit" Text="View/Edit" />
                                <asp:ButtonField AccessibleHeaderText="Delete" CommandName="deleteCustom" HeaderText="Delete" Text="Delete" />
                            </Columns>                         
                        </asp:GridView>

I somehow need to create a condition where an image of a paperclip is shown if the attachmentId value is not Null. Optionally I imagine the query could be re-written to return a true/false value based on if the attachmentId value is null though I'm not certain how to do this. Need a nudge in the right direction on this one.

Thanks!