code: private static Key<?> newKey(Type type, Set<? extends Annotation> qualifiers) {
      if (qualifiers.isEmpty()) {
        return Key.get(type);
      }
      
      // There can be only one qualifier.
      if (qualifiers.size() == 1) {
        for (Annotation first : qualifiers) {
          return Key.get(type, first);
        }
      }
      
      return null;
    }
docs: Creates and returns a {@link Key} for the given {@link Type} and {@link Set} of {@link Annotation}s.