code: public void validate(final List<Throwable> validationErrors) {
          if (this.matchers == null) {
              validationErrors.add(new IllegalArgumentException(
                      "Matchers cannot be null.  There should be at least a !acceptAll matcher"));
          }
          if (this.matchers != null && this.matchers.isEmpty()) {
              validationErrors.add(new IllegalArgumentException(
                      "There are no url matchers defined.  There should be at least a " +
                              "!acceptAll matcher"));
          }
      }
docs: Validate the configuration.
  
  @param validationErrors where to put the errors.