Do a null check to prevent NPEs
 - encountered when adding a registrant to a completed registration
 - a person would not be found, so an NPE would be generated
Merge pull request #313 from CruGlobal/EVENT-140

Prevent NPEs when adding registrant to completed registration
Merge pull request #308 from CruGlobal/EVENT-105

Flatten Sessions
Merge pull request #311 from CruGlobal/EVENT-131

Event 131