Feature Receiver: Add users from list to a group

Question

I have a list 'Users' with a column 'UsersToAdd' of Type "Person or Group" which I like to use for provisioning a SP group 'MyUsers' at the creating of a new site.
I have created a feature receiver for this in my Custom Web Template.

When trying to deploy the feature I get an error on the SPFieldUserValue element:
Object reference not set to an instance of an object

Does anyone have an idea how to refactor this code for use in a Feature receiver? (It works when using it as code behind in a Custom App Page)

int ListID; //ID of item containing the users

string listUrl = string.Format("{0}/Lists/Users", sweb.Url);

SPList list = sweb.GetList(listUrl);
SPListItem item = list.GetItemById(ListID);
SPFieldUserValueCollection Users = (SPFieldUserValueCollection)item["UsersToAdd"];

cweb.AllowUnsafeUpdates = true;
foreach (SPFieldUserValue fuv in Users)
{
cweb.EnsureUser(@fuv.User.LoginName);
cweb.SiteGroups[MyUsers].AddUser(@fuv.User.LoginName, string.Empty, fuv.LookupValue, string.Empty);
}

cweb.AllowUnsafeUpdates = false;  

Answer 1

There is nothing wrong with your code as far as I can see. Therefor I tested your code and the time I get the error you described is when the field "UsersToAdd" in the list is empty(doesn't contain any value). A check for null on "Users" will prevent you from getting the error.

Regards, Anita

Answer 2

Yup, I reckon the third line should be:

SPListItem item = list.GetItemById(ListItemID);

Also, note that you can attach Visual Studio to the W3WP process for debugging - I find that very useful in event handlers.