> A call to withAdditionalAnnotations(null) should be resolved to the method 
> withAdditionalAnnotations(List), shouldn't it?

I'm more worried about code like this:

    Annotation annotation = clazz.getAnnotation(MyAnnotation.class);
    // the above can return null
    builder.withAdditionalAnnotations(annotation)

> And for any other call that adds a null to any part of the list / array, we don't check for null either. 

I think many callers might be surprised to find a null in the list of annotations they get from a `Description`, resulting in a `NullPointerException`. And when that problem happens, it may be difficult to find the root cause because the code to create the description might be far removed from the NPE.