I find it unlikely that request is null, but I can't rule out the possibility, especially when alpha versions are used. Of course a stacktrace of the NPE would maybe give some insights. But generally I can only point you to
Smack XMPP File Transfer · igniterealtime/Smack Wiki · GitHub
which basically says that Smack is open source and XMPP is an open standard, you are therefore able and encouraged to debug the issue yourself.