[This check within the map](https://github.com/adambird/entity_store/blob/get-multiple-entities/lib/entity_store/store.rb#L98-101) happens later in the method after we've gone to fetch the events.

For arguments sake, lets say we passed 100 IDs and one of them didn't exist. Currently, we'd go and fetch the events for the 99 entities that did exist, and then blow up on the check within the `map` throwing away all that stuff we didn't need to fetch.

Doing the check before this line would mean we wouldn't have fetched the events for the 99 entities that did exist.