output: #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);
  		}
  
  		String channel = getChannel();
  
  		if (channel == null || !PATTERN_CHANNEL.matcher(channel).matches()) {
  			throw new IllegalArgumentException(String.format(ERROR_INVALID_CHANNEL, channel));
  		}
  
  		boolean connected = isConnected();
  		Boolean switched = hasSwitched(context, channel, connected);
  		String script = null;
  
  		if (switched == null) {
  			Integer port = getPort();
  			String host = (port != null ? ":" + port : "") + getRequestContextPath(context);
  			String channelId = getReference(SocketChannelManager.class).register(channel, getScope(), getUser());
  			String functions = getOnopen() + "," + getOnmessage() + "," + getOnclose();
  			script = String.format(SCRIPT_INIT, host, channelId, functions, getBehaviorScripts(), connected);
  		}
  		else if (switched) {
  			script = String.format(connected ? SCRIPT_OPEN : SCRIPT_CLOSE, channel);
  		}
  
  		if (script != null) {
  			context.getResponseWriter().write(script);
  		}
  
  		rendered = super.isRendered();
  	}
input: #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);
  		}
  
  		String channel = getChannel();
  
  		if (channel == null || !PATTERN_CHANNEL.matcher(channel).matches()) {
  			throw new IllegalArgumentException(String.format(ERROR_INVALID_CHANNEL, channel));
  		}
  
  		boolean connected = isConnected();
  		Boolean switched = hasSwitched(context, channel, connected);
  		String script = null;
  
  		if (switched == null) {
  			Integer port = getPort();
  			String host = (port != null ? ":" + port : "") + getRequestContextPath(context);
  			String channelId = getReference(SocketChannelManager.class).register(channel, getScope(), getUser());
  			String functions = getOnopen() + "," + getOnmessage() + "," + getOnclose();
  			script = String.format(SCRIPT_INIT, host, channelId, functions, getBehaviorScripts(), connected);
  		}
  		else if (switched) {
  			script = String.format(connected ? SCRIPT_OPEN : SCRIPT_CLOSE, channel);
  		}
  
  		if (script != null) {
  			context.getResponseWriter().write(script);
  		}
  	} 
                              #location 20 
                              #vulnerability type NULL_DEREFERENCE