Handle case of null organizerEmail in changed event

* A recent change assumed that organizerEmail couldn't be null while
  an event was being added.  However, there is an unusual case in
  which it CAN be null, and this CL handles that case
* Regression caused by: SHA 7f448dcd470ac509a85368a84f5a55c346ae7e70
Bug: 2719254
Change-Id: Idb8fc79c898bcd2e53fcc8b3e42d0ba67ba762fa
1 file changed