src/main/java/com/conveyal/gtfs/BaseGTFSCache.java
public T put (String id, File feedFile) throws Exception {
        return put(id, feedFile, null);
    }
public T put (String id, File feedFile) throws Exception {
        return put(id, feedFile, null);
    }
Add a GTFS feed to this cache with the given ID. NB this is not the feed ID, because feed IDs are not
unique when you load multiple versions of the same feed.