bind a viewdata inside dropdown list

Question

i wanna bind a viewdata inside dropdown list , 
i use this way 

@Html.DropDownListFor(model => model.First().KEYWORD_NAME, ViewData["KEYWORD"] as IEnumerable<SelectListItem>, "Select Company Name", new { @class = "form-control" })

 
but i have this error : 

System.ArgumentNullException: 'Value cannot be null.

Parameter name: source

 i don't have any parameter with name source ? 
 i debug the project and i checked that the view data have data inside it 

how i can  fix it ?