#vulnerable code 
                                @Override
    public void startCrackedSession(ProtocolLibLoginSource source, StoredProfile profile, String username) {
        BukkitLoginSession loginSession = new BukkitLoginSession(username, profile);
        plugin.getLoginSessions().put(player.getAddress().toString(), loginSession);
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public void startCrackedSession(ProtocolLibLoginSource source, StoredProfile profile, String username) {
        BukkitLoginSession loginSession = new BukkitLoginSession(username, profile);
        plugin.putSession(player.getAddress(), loginSession);
    }