protected boolean isNull(Stream seekable) {
		if (!this.skip(seekable)) {
			raise(new JsonParseException("prase null value fail,unexpected eof", this.excpetion()));
			return false;
		}

		if ((consume(seekable, 'N') || consume(seekable, 'n')) //
				&& (consume(seekable, 'U') || consume(seekable, 'u')) //
				&& (consume(seekable, 'L') || consume(seekable, 'l')) //
				&& (consume(seekable, 'L') || consume(seekable, 'l'))) {
			return true;
		}

		return false;
	}