docs: public static boolean onCheckMainThread(BooleanSupplier defaultChecker) {
      if (defaultChecker == null) {
        throw new NullPointerException("defaultChecker == null");
      }
      BooleanSupplier current = onCheckMainThread;
      try {
        if (current == null) {
          return defaultChecker.getAsBoolean();
        } else {
          return current.getAsBoolean();
        }
      } catch (Exception ex) {
        throw Exceptions.propagate(ex);
      }
    }