The bug wasn't resolved by the line above.
It was resolved adding the following line in JBossBirtServlet :
Please create a jira issue.
Thanks snjeza !
I didn't had any time to work on this one today, and the fix I suggested breaks on first request (reportContext.getHttpServletRequest() is null on the first call to the servlet).
I don't understand...
I'll work more on this next week and I'll create JIRA when I have a better fix to submit.