System.NullReferenceException: 未将对象引用设置到对象的实例！
using (SPWeb web = site.OpenWeb(webID))
{
SPList list = web.Lists[listID];
SPListItem item = list.GetItemById(itemID); //取到想要设置的记录
if ("UserMulti" == field.TypeAsString) //判断该字段是否设置了“允许多重选择”
{
SPFieldUserValueCollection members = (SPFieldUserValueCollection)item[field.Title]; //取出所有数据内容
foreach (SPFieldUserValue member in members)
{
if (member.User != null) //判断该对象是否是用户类型
{
principal.AddUser(member.User); //添加用户
}
else
{
try
{
SPGroup group = web.SiteGroups[member.LookupValue]; //获取用户组
principal.AddGroup(group); //添加用户组
}
catch
{
continue;
}
}
}
}
