cascalog w/ cascading.avro -- problem

gistfile1.clj

(comment
(defproject project "0.0.1-SNAPSHOT"
  :description "project: analysis framework"
  :dependencies [[org.clojure/clojure "1.4.0"]
                 [cheshire "5.0.0"]
                 [cascalog "1.10.0"]
                 [cascalog-math "0.1.0"]
                 [cascading.avro/avro-scheme "2.1.0"]
              ]
  :dev-dependencies [[org.apache.hadoop/hadoop-core "0.20.2-dev"]]
  :repositories {"conjars.org" "http://conjars.org/repo"}
  :main project.core
  :aot [project.core]))

;;(:import [cascading.avro AvroScheme])

(def avro-file "/project/data/data.avro")
(def avro-scheme (AvroScheme. (Schema/parse (slurp "/project/data/schema.json"))))
(def avro-tap (t/hfs-tap avro-scheme avro-file))

;(def reader (DataFileReader. (clojure.java.io/file avro-file) (GenericDatumReader. (Schema/parse (slurp "/project/data/schema.json")))))
;(doseq [rec (iterator-seq reader)] (prn rec))

(defn avro-q []
  (binding [d/*DEBUG* true]
    (?<- (stdout) [?key]
      ((select-fields avro-tap ["key"]) ?key))))

;; => (avro-q)
;; ...
;; 12/11/29 11:38:32 ERROR stream.TrapHandler: caught Throwable, no trap available, rethrowing
;; cascading.tuple.TupleException: unable to read from input identifier: file:/project/data/data.avro
;;         at cascading.tuple.TupleEntrySchemeIterator.hasNext(TupleEntrySchemeIterator.java:127)
;;         at cascading.flow.stream.SourceStage.map(SourceStage.java:76)
;;         at cascading.flow.stream.SourceStage.run(SourceStage.java:58)
;;         at cascading.flow.hadoop.FlowMapper.run(FlowMapper.java:124)
;;         at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:358)
;;         at org.apache.hadoop.mapred.MapTask.run(MapTask.java:307)
;;         at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.javFlowException local step failed  cascading.flow.planner.FlowStepJob.blockOnJob (FlowStepJob.java:191)
;; a:176)
;; Caused by: org.apache.avro.AvroRuntimeException: Unions may only consist of a concrete type and null in cascading.avro
;;         at cascading.avro.AvroToCascading.fromAvroUnion(AvroToCascading.java:131)
;;         at cascading.avro.AvroToCascading.fromAvro(AvroToCascading.java:58)
;;         at cascading.avro.AvroToCascading.parseRecord(AvroToCascading.java:48)
;;         at cascading.avro.AvroToCascading.fromAvro(AvroToCascading.java:73)
;;         at cascading.avro.AvroToCascading.parseRecord(AvroToCascading.java:48)
;;         at cascading.avro.AvroScheme.source(AvroScheme.java:222)
;;         at cascading.tuple.TupleEntrySchemeIterator.getNext(TupleEntrySchemeIterator.java:140)
;;         at cascading.tuple.TupleEntrySchemeIterator.hasNext(TupleEntrySchemeIterator.java:120)
;;         ... 6 more