Sending a null header or footer value when sending packet 0x47 will result in an NPE, due to the value not being checked before being turned into a formatted string:

    public void handlePlayerListHeaderFooter(S47PacketPlayerListHeaderFooter packetIn)
    {
        this.gameController.ingameGUI.getTabList().setHeader(packetIn.getHeader().getFormattedText().length() == 0 ? null : packetIn.getHeader());
        this.gameController.ingameGUI.getTabList().setFooter(packetIn.getFooter().getFormattedText().length() == 0 ? null : packetIn.getFooter());
    }

The formatted text length is never zero - getFormattedText adds §r even if the provided text is empty - which means that there is no way to remove the header or footer, just make empty text/§r appear. Sending null, if it didn't call getFormattedText first, would work as intended.