Why does InstanceComponentAdapter check if instance is concrete ?

InstanceComponentAdapter extends AbstractComponentAdapter, which checks in its constructor for the concreteness of the component class.
I have a case where this concreteness check fails (still clearly does not get why...), and i was wondering why this test was useful at all for the InstanceComponentAdapter...

I do not know if the test should be removed, but i will try anyway to describe my case hereafter (test case attached):

public interface Descriptor
{
...

public static class DescriptorData

}

I register into pico an instance of type Descriptor$DescriptorData[] and this fails... It work of course ok if i comment the call to checkConcrete in AbstractComponentAdapter constructor...