src/main/java/com/conveyal/gtfs/BaseGTFSCache.java
public T put (Function<GTFSFeed, String> idGenerator, File feedFile) throws Exception {
        return put(null, feedFile, idGenerator);
    }
public T put (Function<GTFSFeed, String> idGenerator, File feedFile) throws Exception {
        return put(null, feedFile, idGenerator);
    }
Add a GTFS feed to this cache where the ID is calculated from the feed itself