combobox not to display the first blank option when selecting an option

[Nessy]

Is there a way to display an blank combobox option (with no value) and when a user click to select an option, this first blank option does not show for selection. After the user choose the option there is no way he can leave the combobox blank again.I was reading and I believe I could use label but I want to know tf there is an specific code for this implementationI am using the html helper\[code\] @Html.DropDownList("tipo_right", new SelectList(Model, "id", "tipoName"), "",new { @class = "validate[required] meddiumField" })\[/code\]Thanks