docs: private static Annotation extractQualifier(Annotation[] annotations,
        Object subject) {
      Annotation qualifier = null;
      for (Annotation a : annotations) {
        if (!IS_QUALIFIER_ANNOTATION.get(a.annotationType())) {
          continue;
        }
        if (qualifier != null) {
          throw new IllegalArgumentException("Too many qualifier annotations on " + subject);
        }
        qualifier = a;
      }
      return qualifier;
    }