Huge bug of jquery ajax !!!
$.ajax(
{
url: xxxx,
data: { name: null, sex: 0 }
......
this ajax will send a request to the server just like xxxx?name=null&sex=0
yes, null is translated to string "null", and in the server side, like php, java, asp.net , name will have a value of string "null", not empty or null string.