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.
$(function () {
// Get value
var returnsValue; // Type: string
returnsValue = $(".selector").wijgrid("option", "nullString");
// Set value
var newValue; // Type: string
$(".selector").wijgrid("option", "nullString", newValue);
});