public static @NotNull Collection<String> getVisitorClasses() {
    Set<String> set = ourClasses;
    if (set != null) return set;

    set = EP_NAME.getExtensionList().stream()
      .map(x -> x.clazz)
      .collect(toSet());
    ourClasses = set;

    return set;
  }
public static @NotNull Collection<String> getVisitorClasses()