null fixes regarding tracking connector info on Event and (de-)serialization

java/com.sap.sailing.domain.shared.android/src/com/sap/sailing/domain/base/impl/StrippedEventImpl.java

@@ -31,6 +31,7 @@ public class StrippedEventImpl extends EventBaseImpl {
             boolean isPublic, UUID id, Iterable<LeaderboardGroupBase> leaderboardGroups, Set<TrackingConnectorInfo> trackingConnectorInfos) {
         super(name, startDate, endDate, venue, isPublic, id);
         this.leaderboardGroups = leaderboardGroups;
+        assert trackingConnectorInfos != null;
         this.trackingConnectorInfos = trackingConnectorInfos;
     }