Exception to be thrown from a FactoryBean's getObject() method
if the bean is not fully initialized yet, for example because it is involved
in a circular reference.
Note: A circular reference with a FactoryBean cannot be solved by eagerly
caching singleton instances like with normal beans. The reason is that
every FactoryBean needs to be fully initialized before it can
return the created bean, while only specific normal beans need
to be initialized - that is, if a collaborating bean actually invokes
them on initialization instead of just storing the reference.