Retrieving An Image From SQL, Test For Null

I have an employee directory application that displays employees in a gridview.  When a record is selected, a new page opens and displays all info about the employee, including their photo.  I have the code working that displays the photos, however, when no photo is present an exception is thrown that "Unable to cast object of type System.DbNull to System.Byte[]".  I'm not sure how to test for no photo before trying to write it out. 

My code is as follows (with no error trapping):
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load, Me.Load

Dim temp As String

Dim connPhoto As System.Data.SqlClient.SqlConnection

Dim connstring As Stringconnstring = Web.Configuration.WebConfigurationManager.ConnectionStrings("connPhoto").ConnectionString

connPhoto = New System.Data.SqlClient.SqlConnection(connstring)temp = Request.QueryString("id")

Dim SqlSelectCommand2 As System.Data.SqlClient.SqlCommand

Dim sqlstring As String

sqlstring = "Select * from dbo.PhotoDir WHERE (CMS_ID = " + temp + ")"SqlSelectCommand2 = New System.Data.SqlClient.SqlCommand(sqlstring, connPhoto)

Try

connPhoto.Open()Dim myDataReader As System.Data.SqlClient.SqlDataReader

myDataReader = SqlSelectCommand2.ExecuteReader

Do While (myDataReader.Read())

Response.BinaryWrite(myDataReader.Item("ImportedPhoto"))

Loop

connPhoto.Close()Catch SQLexec As System.Data.SqlClient.SqlException

Response.Write("Read Failed : " & SQLexec.ToString())

End TryEnd Sub

End Class