Data Controls :: How To Show GridView Image Conditionally

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>

[Code]....

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.