#vulnerable code 
                             @Override
	public void encodeChildren(FacesContext context) throws IOException {
		if (!TRUE.equals(getApplicationAttribute(context, Socket.class.getName()))) {
			throw new IllegalStateException(ERROR_ENDPOINT_NOT_ENABLED);
		}

		if (SocketFacesListener.register(context, this)) {
			String channel = getChannel();

			if (channel == null || !PATTERN_CHANNEL.matcher(channel).matches()) {
				throw new IllegalArgumentException(format(ERROR_INVALID_CHANNEL, channel));
			}

			Integer port = getPort();
			String host = (port != null ? ":" + port : "") + getRequestContextPath(context);
			String channelId = getReference(SocketChannelManager.class).register(channel, getScope(), getUser());
			String functions = getOnopen() + "," + getOnmessage() + "," + getOnclose();
			String behaviors = getBehaviorScripts();
			boolean connected = isConnected();

			String script = format(SCRIPT_INIT, host, channelId, functions, behaviors, connected);
			context.getResponseWriter().write(script);
		}
	} 
                            #location 16 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             @Override
	public void encodeChildren(FacesContext context) throws IOException {
		if (!TRUE.equals(getApplicationAttribute(context, Socket.class.getName()))) {
			throw new IllegalStateException(ERROR_ENDPOINT_NOT_ENABLED);
		}

		if (SocketFacesListener.register(context, this)) {
			String channel = getChannel();

			if (channel == null || !PATTERN_CHANNEL.matcher(channel).matches()) {
				throw new IllegalArgumentException(format(ERROR_INVALID_CHANNEL, channel));
			}

			Integer port = getPort();
			String host = (port != null ? ":" + port : "") + getRequestContextPath(context);
			String channelId = SocketChannelManager.getInstance().register(channel, getScope(), getUser());
			String functions = getOnopen() + "," + getOnmessage() + "," + getOnclose();
			String behaviors = getBehaviorScripts();
			boolean connected = isConnected();

			String script = format(SCRIPT_INIT, host, channelId, functions, behaviors, connected);
			context.getResponseWriter().write(script);
		}
	}