public void MergeInto(IDomainEventStore domainEventStore)
{
if (_mergedStore != null)
throw new InvalidOperationException("This store has already been merged with another store.");
var domainEventsToMerge = RetrieveAndClear();
_mergedStore = domainEventStore;
foreach (var domainEvent in domainEventsToMerge)
_mergedStore.Add(domainEvent);
}