[ACS44] Cherry-pick for CLOUDSTACK-6970

[Kelven Yang]

Daan,

Please cherry-pick following from 4.4-forward to 4.4

commit 06d8d3a03f7a4efc41c45d9f67fd5b7586a78454
Author: Kelven Yang <kelv...@gmail.com>
Date:   Thu May 29 09:35:03 2014 -0700

    CLOUDSTACK-6970: Protect event interpretion from causing NPE exception


Thanks
Kelven