NullPointerException for simple query about datahike HOT 1 CLOSED

#datahike/Datom [1 :user/name "max" 536870913 true]
#datahike/Datom [9 :comment/upvotes 1 536870914 true]

  (let [schema {:user/name {:db/type   :db.type/string
                            :db/unique :db.unique/identity}
                :comment/upvotes {:db/valueType   :db.type/ref
                                  :db/cardinality :db.cardinality/many}}
        dburl "datahike:file:///tmp/example.db"
        _     (datahike.api/delete-database dburl)
        _     (datahike.api/create-database-with-schema dburl schema)
        conn  (datahike.api/connect dburl)]

    (datahike.migrate/import-db conn "/tmp/example.edn")

    (d/q '[:find ?cid
           :where [?cid :comment/upvotes _]]))