I suggest we fix it something like this:

if( $t_filter_user_value != META_FILTER_NONE && $t_filter_user_value != ALL_USERS ) {
    # Make sure the filter value exists in the list
    $t_row = user_get_row( $t_filter_user_value );
    if( $t_row ) {
        $t_users_ids[] = $t_filter_user_value;
        $t_users_list[] = user_get_name_from_row( $t_row );
        $t_sort[] = user_get_name_for_sorting_from_row( $t_row );
    }
}

The problem can be reproduced by manually altering the MANAGE_CONFIG_COOKIE's value to specify a non-existing user id.

In real life, given that a filter in the admin page for a specific user has been applied (saved in the cookie), returning to the page after said user has been deleted should trigger the error also.

I think a more appropriate fix than what you suggested in 0035064:0069519 would be to check for the user id's existence after retrieving it from the cookie; if not found, we could default to ALL_USERS, following the same logic that is already implemented for projects. I'll submit a PR later.

if not found, we could default to ALL_USERS

I think this code creates a filter list, so ALL_USERS is added to that list anyway.

if not found, we could default to ALL_USERS

I think this code creates a filter list, so ALL_USERS is added to that list anyway.

Indeed. So the logic should be:

• retrieve current user id from cookie
• if not an existing user, use ALL_USERS as default (NEW)
• build the list for the select (including any and ALL_USERS)
• if current user id is not in the list, add it
• render the list with current user selected

I'll submit a PR later.

I fixed the code, and then forgot to push the branch and create the PR...
Done now https://github.com/mantisbt/mantisbt/pull/2065