>RepositoryBase has this code
>
>

> public virtual T GetById(object id)
>        {
>            return _dbSet.Find(id);
>        }
>

Raises more questions than it answers :-{
The class containing the virtual is obviously generic so how is it defined. I'd guess 'T:Class' and that the return from GetById() is an instance of Operator.
I'd also guess that the sub class is defined as inheriting

: parent<Operator>

?
Are those assumptions correct?

IAC, from what you say is doesn't sound as if an exception is being thrown - why not just step the call to see what is happening?