how to Insert null value in image column

Hi,
how can  insert null value in image column.i using sql server 2005 and in my database i have column image and datafield id image.when i browse a image and insert it then it is working but when i insert it without image then it is not saved.an error ocure-Operand type clash: nvarchar is incompatible with image.
I INSERT LIKE
If fileUpload1.HasFile Then Dim File As HttpPostedFile = fileUpload1.PostedFile imgByte = New [Byte](File.ContentLength - 1) {} File.InputStream.Read(imgByte, 0, File.ContentLength) myNews.Image = imgByte Else myNews.Image = imgByte
 
END IF
PLEASE HELP ME.
THANKING YOU
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