How can i insert NULL value in db column from vb.net code behind sql query?

myCommand.CommandText = "UPDATE db_admin.tblContent " _
            & "SET Headline='" & valHead & "', " _
            & "Standfirst='" & valStandfirst & "'," _
            & "Thumbnail='" & valThumbnail & "'," _
            & "MainImage='" & valMainImage & "'," _
            & "MetaDescription='" & valMetaDescription & "'," _
            & "MetaKeyWords='" & valMetaKeyWords & "'," _
            & "Article='" & valArticle & "'," _
            & "URLTitle='NULL' " _
            & "WHERE ContentID = " & qID




      myCommand.CommandText = "UPDATE db_admin.tblContent " _
            & "SET Headline='" & valHead & "', " _
            & "Standfirst='" & valStandfirst & "'," _
            & "Thumbnail='" & valThumbnail & "'," _
            & "MainImage='" & valMainImage & "'," _
            & "MetaDescription='" & valMetaDescription & "'," _
            & "MetaKeyWords='" & valMetaKeyWords & "'," _
            & "Article='" & valArticle & "'," _
            & "URLTitle='' " _
            & "WHERE ContentID = " & qID

I tried the queries above but one leave the cell empty while other leave the cell will string 'NULL' but its not the null you get when you manually type NULL by opening the table in edit mode.