private URL validateUrl(URL url) {
		if (url == null) {
			return HELP_NOT_FOUND_PAGE_URL;
		}

		try {
			InputStream inputStream = url.openStream();
			inputStream.close();
			return url;
		}
		catch (IOException e) {
			// handled below
		}

		return HELP_NOT_FOUND_PAGE_URL;
	}
This forces page to be redisplayed when location has not changed
Ghidra/Framework/Docking/src/main/java/docking/help/HelpManager.java