code: private Statement withClassRules(Statement statement) {
          List<TestRule> classRules = classRules();
          return classRules.isEmpty() ? statement :
                  new RunRules(statement, classRules, getDescription());
      }
docs: Returns a {@link Statement}: apply all
  static fields assignable to {@link TestRule}
  annotated with {@link ClassRule}.
  
  @param statement the base statement
  @return a RunRules statement if any class-level {@link Rule}s are
  found, or the base statement