QueryInterceptor exception

[RequiresAuthentication]

I have a QueryInterceptor that looks like the below.  Basically, all it is doing is getting the current AppUserEntity and using that in the Filter.  This all works fine until I put the [RequiresAuthentication] attribute on the AppUserEntity.  When I do that, I get an EntityServerError that says : Parameter 'principal' cannot be null.  The error occurs during the execution of AppUserEntity query.
public class QueryInterceptor : EntityServerQueryInterceptor
    {
        protected override bool FilterQuery()
        {
            if (this.Query.ElementType == typeof(EmailAccountEntity))
            {
                var currentUser = this.GetCurrentAppUserEntity();
                if (currentUser != null)
                {
                    QueryFilters.AddFilter<EmailAccountEntity>(q => q.Where(c => c.OwnedBy == currentUser.Id));
                }
                else
                {
                    //Will return no records.
                    QueryFilters.AddFilter<EmailAccountEntity>(q => q.Where(c => c.OwnedBy == -1));
                }
            }
            return base.FilterQuery();
        }
        protected AppUserEntity GetCurrentAppUserEntity()
        {
            string name = this.Principal.Identity.Name;
            IEntityQuery<AppUserEntity> query = 
                this.EntityManager.GetQuery<AppUserEntity>()
                .Where(user => user.AspNetDbUserName == name );

            var appUsers = this.EntityManager.ExecuteQuery<AppUserEntity>(query);  //This is where the error occurs.

            return appUsers.FirstOrDefault();

        }
    }

I like having the [RequiresAuthentication] attribute because it ensure that no-one is going to be getting to those entities without being logged in.  I could manually do this in the QueryInterceptor, but would prefer the attribute as it's less error prone.

I did some testing and any Entity type that is queried in the QueryInterceptor throws the same error if the RequiresAuthentication attribute is used on it.

Greg