How to check value(if it is null or not) in processFormRequest

if (pageContext.getParameter("ApplyBtn") != null){

         OAViewObject voh = (OAViewObject)am.findViewObject("XxVO1");
         try {
             voh.getCurrentRow().getAttribute("XxColumnName").toString();
         } catch (NullPointerException e) {
             throw new OAException("XxColumnName Name is Required", OAException.ERROR);
         }
}