lein cloverage failed but lein test passed

with lein cloverage:
Testing XXXX.XXXX.XXXX.common.nmlg2-iim-convertor-test
ERROR in (nmlg2-to-iim-test) (Reflector.java:80)
Uncaught exception, not in assertion.
expected: nil
  actual: java.lang.IllegalArgumentException: No matching method found: alength
 at clojure.lang.Reflector.invokeMatchingMethod (Reflector.java:80)
    clojure.lang.Reflector.invokeStaticMethod (Reflector.java:207)
    clojure.core$alength.invoke (core.clj:3512)
    reuters.pipeline.iim.DataSet.to_bytes (reuters/pipeline/iim.clj:45)
    reuters.pipeline.iim$eval9077$fn__9078$G__9069__9080.invoke (reuters/pipeline/iim.clj:31)
    reuters.pipeline.iim$eval9077$fn__9078$G__9068__9083.invoke (reuters/pipeline/iim.clj:31)
    reuters.pipeline.iim.DataSet.write (reuters/pipeline/iim.clj:57)
    reuters.pipeline.iim$eval9077$fn__9100$G__9065__9103.invoke (reuters/pipeline/iim.clj:31)
    reuters.pipeline.iim$eval9077$fn__9100$G__9064__9107.invoke (reuters/pipeline/iim.clj:31)
    reuters.pipeline.iim$output_to_file$fn__9568.invoke (reuters/pipeline/iim.clj:696)
    clojure.core$map$fn__4207.invoke (core.clj:2485)
    clojure.lang.LazySeq.sval (LazySeq.java:42)
    clojure.lang.LazySeq.seq (LazySeq.java:60)
    clojure.lang.RT.seq (RT.java:484)
    clojure.core$seq.invoke (core.clj:133)
    clojure.core$dorun.invoke (core.clj:2780)
    reuters.pipeline.iim$output_to_file.invoke (reuters/pipeline/iim.clj:696)
    reuters.pipeline.processors.common.nmlg2_iim_convertor$convert.invoke (reuters/pipeline/processors/common/nmlg2_iim_convertor.clj:87)
    reuters.pipeline.processors.common.nmlg2_iim_convertor_test/fn (nmlg2_iim_convertor_test.clj:53)
    clojure.test$test_var$fn__7145.invoke (test.clj:701)
    clojure.test$test_var.invoke (test.clj:701)
    clojure.test$test_all_vars$fn__7149$fn__7156.invoke (test.clj:717)
    clojure.test$default_fixture.invoke (test.clj:671)
    clojure.test$test_all_vars$fn__7149.invoke (test.clj:717)
    reuters.pipeline.processors.common.nmlg2_iim_convertor_test$ft.invoke (nmlg2_iim_convertor_test.clj:36)
    clojure.test$compose_fixtures$fn__7139$fn__7140.invoke (test.clj:678)
    clojure.test$default_fixture.invoke (test.clj:671)
    clojure.test$compose_fixtures$fn__7139.invoke (test.clj:678)
    clojure.test$test_all_vars.invoke (test.clj:713)
    clojure.test$test_ns.invoke (test.clj:736)
    clojure.core$map$fn__4207.invoke (core.clj:2485)
    clojure.lang.LazySeq.sval (LazySeq.java:42)
    clojure.lang.LazySeq.seq (LazySeq.java:60)
    clojure.lang.ChunkedCons.chunkedNext (ChunkedCons.java:59)
    clojure.core$chunk_next.invoke (core.clj:660)
    clojure.core$reduce1.invoke (core.clj:895)
    clojure.core$reduce1.invoke (core.clj:887)
    clojure.core$merge_with.doInvoke (core.clj:2702)
    clojure.lang.RestFn.applyTo (RestFn.java:139)
    clojure.core$apply.invoke (core.clj:619)
    clojure.test$run_tests.doInvoke (test.clj:751)
    clojure.lang.RestFn.applyTo (RestFn.java:137)
    clojure.core$apply.invoke (core.clj:617)
    cloverage.coverage$_main.doInvoke (coverage.clj:153)
    clojure.lang.RestFn.invoke (RestFn.java:3894)
    clojure.lang.Var.invoke (Var.java:527)
    user$eval3$fn__5.invoke (NO_SOURCE_FILE:1)
    user$eval3.invoke (NO_SOURCE_FILE:1)
    clojure.lang.Compiler.eval (Compiler.java:6619)
    clojure.lang.Compiler.eval (Compiler.java:6609)
    clojure.lang.Compiler.eval (Compiler.java:6582)
    clojure.core$eval.invoke (core.clj:2852)
    clojure.main$eval_opt.invoke (main.clj:308)
    clojure.main$initialize.invoke (main.clj:327)
    clojure.main$null_opt.invoke (main.clj:362)
    clojure.main$main.doInvoke (main.clj:440)
    clojure.lang.RestFn.invoke (RestFn.java:421)
    clojure.lang.Var.invoke (Var.java:419)
    clojure.lang.AFn.applyToHelper (AFn.java:163)
    clojure.lang.Var.applyTo (Var.java:532)
    clojure.main.main (main.java:37)

with lein test: (no errors)
lein test xxxx.xxxx.xxxx.common.transformer-processor-test

lein test xxxx.xxxx.xxxx.common.nmlg2-iim-convertor-test

lein test xxxx.xxxx.xxxx.common.klt-packager-test