code: protected Configurations merge(Configurations other) {
  		Set<Class<?>> mergedClasses = new LinkedHashSet<>(getClasses());
  		mergedClasses.addAll(other.getClasses());
  		return merge(mergedClasses);
  	}
docs: Merge configurations from another source of the same type.
  @param other the other {@link Configurations} (must be of the same type as this
  instance)
  @return a new configurations instance (must be of the same type as this instance)