code: static List<JClass> allConcreteClasses(Set<ClassOutline> classes, Set<JClass> directClasses) {
          List<JClass> results = new ArrayList<>();
          classes.stream()
                  .filter(classOutline -> !classOutline.target.isAbstract())
                  .forEach(classOutline -> {
              JClass implClass = classOutline.implClass;
              results.add(implClass);
          });
          results.addAll(directClasses);
  
          return results;
      }
docs: Returns all of the concrete classes plus the direct classes passed in
  @param classes collection of clases to test to see if they're abstract or concrete
  @param directClasses set of classes to append to the list of concrete classes
  @return list of concrete classes