[jQuery] How to remove 'null' or replace it with "" for the returned data?

[jQuery] How to remove 'null' or replace it with "" for the returned data?


$.getJSON('/MailDatQueryJsonAction',
{mailDatHeaderID:maildatheaderid},function(data){
             $('#historyJobID').attr("value",data.historyJobID);
}
In jquery-1.2.1.js, when data.historyJobID is empty,it will return
"",correct!!
But in jquery-1.3.2.min.js, it returns "null".
Who can help me resolve this problem?