Remove redundant logic from DescriptionBuilder

Current implementation is based on the approach usually used to enforce at least one argument on varargs method invocation. In a given context such an enforcement has no meaning as invoking withAdditionalAnnotations() with no arguments is the same nonsense for the author as invoking withAdditionalAnnotations(null). There are also no any null-checking and the consequences of both forms of invocations are the same.  Motivation is to remove redundant ArrayList instance construction and some CPU cycles.