How To Hide Items Within A Datalist If Values Are NULL

For example in my datalist if Eval("OptionJ").Tostring = Null I would like the function GetVisible to set visibility of the radio button to false like so:

<input name="Q<%#Eval("ID")%>" type="radio" value="J" visible="<%# GetVisible(Eval("OptionJ").ToString()) %>">
<%#Server.HtmlEncode(Eval("OptionJ").ToString())%>
</option><br />

I then have a codebehind function like so:

Protected Function GetVisible(ByVal Evalresult As String) As String
If Evalresult = Nothing Then
Return "False"
Else
Return "True"
End If
End Function

I have also tried checking EvalResult = String.empty

In the outputted html the visible status is being set to false...

<input name="Q3" type="radio" value="J" visible="False">

But it is still displayed on the page!