cookie为空时，parseCookie函数报错

exports.parseCookie = function (cookieStr) {
var tmpArr = cookieStr.split('; ');
var obj = {};
tmpArr.forEach(function(item, index) {
if (item.match(/^[^=]*(?==)/)) {
obj[item.match(/^[^=]*(?==)/)[0]] = item.match(/=(\S*)/)[1]
}
});
return obj;
};

Start at the parseCookie function shown in the issue and reproduce the failure with an empty cookie string. Confirm the change no longer throws while preserving the function's existing cookie-parsing behavior.

Written by the indexing model from the issue text.