Cell values equal to this property value are considered null values. Use this option if you want to change default representation of null values (empty strings) with something else.

//値を取得する
var value; //タイプ： string
value = $(".selector").c1gridview("option", "nullString");

//値を設定します
var newValue; //タイプ： string
$(".selector").c1gridview("option", "nullString", newValue);

var nullString : string;

$("#element").wijgrid({ nullString: "" });