Symfony2 Doctrine2 trouble with optional one to one relation

Question

I have a problem with Doctrine2 in Symfony2 and two relationed entities.

There is a user-entity that can (not must) have a usermeta-entity referenced which

Answer 1

I got the error message "spl_object_hash() expects parameter 1 to be object, null given in..." while trying the same thing. I tried to define a bidirectional One to One relationship while the inversed value could be null. This gave the error message. Taking away the inversed side of the relationship solved the problem. It is a pity that Zero or One to One relationships aren't supported.