NHibernate LazyInitializationException being raised in one class and not in another

Question

I have two classes. Both classes have similar structure in that they both have a many-to-many relation. But strangely enough the second class is causing a LazyInitializationException. I've no clue why? Both are fetching data from an intermediate table but how come the second class is only producing the error?

public class TaskMap : VersionedClassMap<Task>
{
    public TaskMap()
    {
        Id(x => x.TaskId);
        Map(x => x.Subject).Not.Nullable();
        Map(x => x.StartDate).Nullable();
        Map(x => x.DueDate).Nullable();
        Map(x => x.DateCompleted).Nullable();

        References(x => x.Status, "StatusId");
        References(x => x.Priority, "PriorityId");
        References(x => x.CreatedBy, "CreatedUserId");

        HasManyToMany(x => x.Users)
            .Access.ReadOnlyPropertyThroughCamelCaseField(Prefix.Underscore)
            .Table("TaskUser")
            .ParentKeyColumn("TaskId")
            .ChildKeyColumn("UserId");

        HasManyToMany(x => x.Categories)
            .Access.ReadOnlyPropertyThroughCamelCaseField(Prefix.Underscore)
            .Table("TaskCategory")
            .ParentKeyColumn("TaskId")
            .ChildKeyColumn("CategoryId");
    }
}

and

public class LocationMap: VersionedClassMap<Location>
{
    public LocationMap()
    {
        Id(x => x.LocationId);
        Map(x => x.Name).Not.Nullable();
        Map(x => x.Address).Nullable();
        Map(x => x.City).Nullable();
        Map(x => x.State).Nullable();
        Map(x => x.Country).Nullable();
        Map(x => x.Pincode).Nullable();

        HasManyToMany(x => x.Departments)
            .Access.ReadOnlyPropertyThroughCamelCaseField(Prefix.Underscore)
            .Table("LocationDepartment")
            .ParentKeyColumn("LocationId")
            .ChildKeyColumn("DepartmentId"); //.Fetch.Join(); Adding this removes the error
    }
}

EDIT:

Here is the link for the project.

Answer 1

You didn't supply any code how you use it with ISession, but such exception occurs when you trying to read uninitialized lazy property/collection on entity associated with closed session. Keep session alive until you work with entities. UPDATE
I cannot figure out in a reasonable time where and when session is closed. The best you can do is to use eager loading in your queries. Here's an example for LocationController:

public IEnumerable<Location> Get()
{
    return _session
            .QueryOver<Data.Model.Location>()
            .Fetch(x => x.Departments).Eager
            .List()
            .Select(_locationMapper.CreateLocation);
}